Biomedical subjects

T Crow

Publications and source records attributed to T Crow.

At least 19 recordsLinked to original sources

PubMed2001

Characterization of the human Xq21.3/Yp11 homology block and conservation of organization in primates.

The Xq21.3/Yp11 homology block on the human sex chromosomes represents a recent addition to the Y chromosome through a transposition event. It is believed that this transfer of material occurred after the divergence of the hominid lineage from other great apes. In this paper we investigate the structure and evolution of the block through fluorescence in situ hybridisation, contig assembly, the polymerase chain reaction, exon trapping, sequence comparison, and annotation of sequence data. The overall structure is well conserved between the human X chromosome and the Y chromosome as well as between the X chromosomes from different primates. Although the sequence data reveal a high level of nucleotide sequence identity for the human X and Y, there are regions of significant divergence, such as that around the marker DXS214. These are presumably the consequence of multiple rearrangements during evolution and are of particular importance with respect to the potential gene content in this segment of the interval.

Animals↗

PubMed2001

Serotonin activation of the ERK pathway in Hermissenda: contribution of calcium-dependent protein kinase C.

The mitogen-activated protein kinase (MAPK) cascade is an important contributor to synaptic plasticity and learning in both vertebrates and invertebrates. In the nudibranch mollusk Hermissenda, phosphorylation and activation of the extracellular signal-regulated protein kinase (ERK), a key member of a MAPK cascade, is produced by one-trial and multitrial Pavlovian conditioning. Several signal transduction pathways that are activated by 5-hydroxytryptamine (5-HT) and may contribute to conditioning have been identified in type B photoreceptors. However, the regulation of ERK activity by 'upstream' signaling molecules has not been previously investigated in Hermissenda. In the present study we examined the role of protein kinase C (PKC) in the serotonin (5-HT) activation of the ERK pathway. The phorbol ester TPA produced an increase in ERK phosphorylation that was blocked by the PKC inhibitors GF109203X or Gö6976. TPA-dependent ERK phosphorylation was also blocked by the MEK1 inhibitors PD098059 or U0126. The increased phosphorylation of ERK by 5-HT was reduced but not blocked by pretreatment with the calcium chelator BAPTA-AM or pretreatment with Gö6976 or GF109203X. These results indicate that Ca(2+)-dependent PKC activation contributes to ERK phosphorylation, although a PKC-independent pathway is also involved in 5-HT-dependent ERK phosphorylation and activation.

Animals↗

PubMed2000

Identification of a 24 kDa phosphoprotein associated with an intermediate stage of memory in Hermissenda.

A requirement for protein synthesis is a critical feature in dissociating different phases of memory. However, in examples of cellular and synaptic plasticity in which an early or intermediate requirement for protein synthesis has been implicated, specific proteins have not been identified. Here we report the identification of a 24 kDa phosphoprotein (CSP24) associated with an intermediate stage of memory, distinct from short-term memory, detected after one-trial conditioning of Hermissenda. CSP24, initially identified from (32)PO(4)-labeled proteins resolved by two dimensional (2-D) PAGE, was excised from multiple Coomassie blue-stained 2-D gels and subjected to reverse phase HPLC and automated sequence analysis. The sequenced peptides exhibited a homology to the beta-thymosin family of actin-binding protein. Anti-CSP24 antibody recognized CSP24 on 1- and 2-D gels by Western blot analysis. Labeled CSP24 immunoprecipitated with anti-CSP24 antibody revealed that significantly more (32)PO(4) was incorporated in preparations that received one-trial conditioning compared with unpaired controls. In contrast, labeled CSP24 immunoprecipitated with anti-CSP24 from conditioned and unpaired control preparations receiving a procedure that only produced short-term enhanced excitability did not exhibit differences in (32)PO(4) incorporation into the immunoprecipitates. These results show that a specific identified phosphoprotein is associated with an intermediate stage of memory for one-trial conditioning in Hermissenda.

Animals↗

PubMed2000

Monosynaptic connections between identified A and B photoreceptors and interneurons in Hermissenda: evidence for labeled-lines.

The cellular and synaptic organization of the eye of the nudibranch mollusk Hermissenda is well-documented. The five photoreceptors within each eye are mutally inhibitory and can be classified into two types: A and B based on electrophysiological and anatomical criteria. Two of the three type B and two type A photoreceptors can be further identified according to their medial or lateral positions within each eye. In addition to reciprocal synaptic connections between photoreceptors, photoreceptors also project to second-order neurons in the cerebropleural ganglion. The second-order neurons receive convergent synaptic input from two additional sensory pathways; however, it has not been previously established if lateral A, lateral B, or medial B photoreceptors converge onto the same second-order neurons. To determine the specific synaptic organization of these components of the visual system, we have examined monosynaptic connections between identified lateral and medial type A and B photoreceptors and second-order cerebropleural (CP) interneurons. We found that monosynaptic connections between identified lateral A and lateral and medial B photoreceptors and CP interneurons follow a labeled-line principle. Illumination of the eyes or extrinsic depolarizing current applied to identified photoreceptors evoked excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs, respectively) in different CP interneurons. The PSPs in CP interneurons followed one-for-one spikes in the photoreceptors and could be elicited in artificial seawater solutions containing high divalent cations. Identified photoreceptors projected to more than one CP interneuron and expressed both excitatory and inhibitory connections with the different CP interneurons. In examples where a monosynaptic connection between a lateral B photoreceptor and a CP interneuron was identified, lateral A, medial A, or medial B photoreceptors did not project to the same CP interneuron. Moreover, when connections between medial B and CP interneurons were identified, lateral A, medial A, and lateral B connections were not found to project to the same CP interneuron. Similar results were obtained for a lateral A and CP interneuron connection. These results indicate that divergent labeled-lines exist between specific photoreceptors and second-order CP interneurons and potential convergence of synaptic input from primary and secondary elements of the visual system must occur at sites that are postsynaptic to the CP interneurons.

Action Potentials↗

PubMed1999

Anticipation in schizophrenia: a review and reconsideration.

There have been several reports on anticipation and schizophrenia, and the purpose of the present article is to review the literature and present data from an ongoing family study of schizophrenia. The published data find on average a 10-year difference in the age of onset between the parental and offspring generation in family sets that have been ascertained for a genetic linkage study. The biases inherent in such studies include the biases of ascertainment that were described by Penrose [1948]. Several investigators have searched for evidence of enlarged triplet repeats, and some find evidence consistent with expanded triplet repeats, whereas others do not. In any event the phenomenon of anticipation in schizophrenia appears to be consistently found and an explanation is needed. Data are presented from pairwise analyses using intergenerational pairs from 61 pedigrees with schizophrenia showing evidence of anticipation as well as the fertility bias. Anticipation was found in aunt:niece/nephew pairs (14.5 years) but not in uncle:niece/nephew pairs (0.5 years). The sex difference in age of onset was accentuated in uncles versus aunts (8.5 years), present in parents (4.5 years), but absent in the proband generation. Therefore, there appears to be an interaction within families between age of onset and sex that deserves further investigation. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:686-693, 1999.

Adolescent↗

PubMed1999

Protein synthesis-dependent and mRNA synthesis-independent intermediate phase of memory in Hermissenda.

The conditioned stimulus pathway in Hermissenda has been used to examine the time-dependent mechanisms of memory consolidation following one-trial conditioning. Here we report an intermediate phase of memory consolidation following one-trial conditioning that requires protein synthesis, but not mRNA synthesis. In conditioned animals, enhanced excitability normally expressed during an intermediate phase of memory was reversed by the protein synthesis inhibitor anisomycin, but not by the mRNA synthesis inhibitor 5, 6-dichloro-1-beta-D-ribobenzimidazole (DRB). Associated with the intermediate phase of memory is an increase in the phosphorylation of a 24-kDa protein. Anisomycin present during the intermediate phase blocked the increased phosphorylation of the 24-kDa phosphoprotein, but did not block the increased phosphorylation of other proteins associated with conditioning or significantly change their baseline phosphorylation. DRB did not reverse enhanced excitability or decrease protein phosphorylation expressed during the intermediate phase of memory formation, but it did reverse enhanced excitability 3.5 h after conditioning. Phosphorylation of the 24-kDa protein may support enhanced excitability during the intermediate phase, in the transition period between short- and long-term memory.

Analysis of Variance↗

PubMed1998

Expression of different types of inward rectifier currents confers specificity of light and dark responses in type A and B photoreceptors of Hermissenda.

Each eye of the mollusc Hermissenda consists of five photoreceptors, two type A and three type B cells. Type A cells are quiescent, whereas B cells are spontaneously active in the dark. Differences in the intrinsic membrane properties of type A and B photoreceptors were studied using voltage- and current-clamp techniques. The current density of a Ni2+-sensitive, low-voltage activated Ca2+ current was similar in the two cell types. However, type B cells express an inward rectifier current (Ih) that has different permeation and pharmacological properties from the inward rectifier current in type A cells. The current in the B cells was time-dependent and was blocked by Cs+. Na+ and K+ were the charge carriers for Ih. The inward rectifier current in A cells (IK1) was time-independent, was selectively permeable to K+, and was blocked by Ba2+. Ni2+ reduced the spontaneous spike activities of type A and B cells, whereas Cs+ produced membrane hyperpolarization and reduced the spike activities of dark-adapted B cells. The application of both Cs+ and Ni2+ completely blocked dark-adapted spontaneous activities of B cells. Moreover, Ba2+ increased the excitability of type A cells but not B cells. Hence, differential expression of the two distinct inward rectifiers found in type A and B cells contributes to differences in their intrinsic membrane properties. Because changes in the excitability of the two cell types are correlates of conditioning in Hermissenda, modulation of these underlying currents may play a major role during conditioning-induced plasticity.

Animals↗

PubMed1998

Phosphorylation of mitogen-activated protein kinase by one-trial and multi-trial classical conditioning.

The pathway supporting the conditioned stimulus (CS) is one site of plasticity that has been studied extensively in conditioned Hermissenda. Several signal transduction pathways have been implicated in classical conditioning of this preparation, although the major emphasis has been on protein kinase C. Here we provide evidence for the activation and phosphorylation of a mitogen-activated protein kinase (MAPK) pathway by one-trial and multi-trial conditioning. A one-trial in vitro conditioning procedure consisting of light (CS) paired with the application of 5-HT results in the increased incorporation of 32PO4 into proteins detected with two-dimensional gel electrophoresis. Two of the phosphoproteins have molecular weights of 44 and 42 kDa, consistent with extracellular signal-regulated protein kinases (ERK1 and ERK2). Phosphorylation of the 44 and 42 kDa proteins by one-trial conditioning was inhibited by pretreatment with PD098059, A MEK1 (ERK-Activating kinase) inhibitor. Assays of ERK activity with brain myelin basic protein as a substrate revealed greater ERK activity for the group that received one-trial conditioning compared with an unpaired control group. Western blot analysis of phosphorylated ERK using antibodies recognizing the dually phosphorylated forms of ERK1 and ERK2 showed an increase in phosphorylation after one-trial conditioning compared with unpaired controls. The increased phosphorylation of ERK after one-trial conditioning was blocked by pretreatment with PD098059. Hermissenda that received 10 or 15 conditioning trials showed significant behavioral suppression compared with pseudo-random controls. After conditioning and behavioral testing, the conditioned animals showed significantly greater phosphorylation of ERK compared with the pseudo-random controls. These results show that the ERK-MAPK signaling pathway is activated in Pavlovian conditioning of Hermissenda.

Animals↗

PubMed1997

Synaptic enhancement and enhanced excitability in presynaptic and postsynaptic neurons in the conditioned stimulus pathway of Hermissenda.

Identified type A photoreceptors of Hermissenda express differential effects of classical conditioning. Lateral type A photoreceptors exhibit an increase in excitability to both the conditioned stimulus (CS; light) and extrinsic current. In contrast, medial type A photoreceptors do not express enhanced excitability, but do show enhancement of the medial B to medial A synaptic connection. Therefore, both enhanced excitability and changes in synaptic strength may contribute to long-term plasticity underlying classical conditioning. The activation of protein kinase C (PKC) is involved in the induction of enhanced excitability of identified type B photoreceptors produced by one-trial conditioning and the expression of enhanced excitability in B photoreceptors after multitrial classical conditioning. We have examined a possible role for persistent kinase activity in the expression of enhanced excitability in lateral type A photoreceptors and enhancement of the medial B to medial type A synaptic connection after classical conditioning. Injection of the PKC inhibitor peptide PKC(19-36) into medial type B photoreceptors of conditioned animals did not significantly change the amplitude of medial A IPSPs elicited by single spikes in the medial B photoreceptor. Injections of PKC(19-36) into medial B photoreceptors of pseudorandom controls also did not significantly change the amplitude of IPSPs recorded from the medial A photoreceptor. In contrast, spikes elicited by extrinsic current in lateral type A photoreceptors of conditioned animals were significantly reduced in frequency after intracellular injection of PKC(19-36) as compared with pseudorandom controls. Injection of the noninhibitory analog peptide [glu27]PKC(19-36) did not affect excitability. Thus, enhanced excitability in the lateral A photoreceptor of conditioned animals seems to be influenced, in part, by a constitutively active kinase or a persistent kinase activator, whereas synaptic enhancement of the connection between the medial B and medial A photoreceptors of conditioned animals may involve a different mechanism.

Action Potentials↗

PubMed1997

Long-term enhancement but not short-term in Hermissenda is dependent upon mRNA synthesis.

The reversible transcription inhibitor 5,6-dichloro-1-beta-D-ribobenzimidazole (DRB) was used to examine the contribution of mRNA synthesis to long-term enhancement (LTE) following one-trial conditioning of Hermissenda. Inhibition of mRNA synthesis by DRB or inhibition of protein synthesis by anisomycin did not significantly affect the induction and maintenance of short-term enhancement (STE) examined 1 h after one-trial conditioning. In contrast to the absence of an effect of the inhibitors on STE, LTE was blocked by DRB or anisomycin applied shortly before and during the presentation of the conditioning trial. Consistent with previous reports, animals that received an unpaired CS and US did not exhibit LTE. In addition, a control group that received a concentration of DRB (10(-7) M) that does not significantly affect mRNA synthesis exhibited typical LTE when tested 24 h postconditioning. These results demonstrate that the induction of LTE produced by one-trial conditioning is dependent upon transcription and the regulation of gene expression.

Animals↗

PubMed1997

Time-dependent changes in excitability after one-trial conditioning of Hermissenda.

The visual system of Hermissenda has been studied extensively as a site of cellular plasticity produced by classical conditioning. A one-trial conditioning procedure consisting of light paired with the application of serotonin (5-HT) to the exposed, but otherwise intact, nervous system produces suppression of phototactic behavior tested 24 h after conditioning. Short- and long-term enhancement (STE and LTE) of excitability in identified type B photoreceptors is a cellular correlate of one-trial conditioning. LTE can be expressed in the absence of STE suggesting that STE and LTE may be parallel processes. To examine the development of enhancement, we studied its time-dependent alterations after one-trial conditioning. Intracellular recordings from identified type B photoreceptors of independent groups collected at different times after conditioning revealed that enhanced excitability follows a biphasic pattern in its development. The analysis of spikes elicited by 2 and 30 s extrinsic current pulses at different levels of depolarization showed that enhancement reached a peak 3 h after conditioning. From its peak, excitability decreased toward baseline control levels 5-6 h after conditioning followed by an increase to a stable plateau at 16 to 24 h postconditioning. Excitability changes measured in cells from unpaired control groups showed maximal changes 1 h posttreatment that rapidly decremented within 2 h. The conditioned stimulus (CS) elicited significantly more spikes 24 h postconditioning for the conditioned group as compared with the unpaired control group. The analysis of the time-dependent development of enhancement may reveal the processes underlying different stages of memory for this associative experience.

Analysis of Variance↗

PubMed1996

Protein kinase and G-protein regulation of Ca2+ currents in Hermissenda photoreceptors by 5-HT and GABA.

The effects of serotonin (5-HT) and GABA on two Ca2+ currents, a transient low-voltage-activated current (tLVA) and a sustained high-voltage-activated current (sHVA) were examined in isolated photoreceptors of Hermissenda. The sHVA current was blocked by 5-HT and reduced by activation of protein kinase C (PKC) with phorbol 12-myristate 13-acetate. The effects of 5-HT were transiently reversed by staurosporine and partially blocked by the PKC inhibitor peptide [PKC(19-36)]. GABA enhanced both the tLVA and sHVA currents at low concentrations (5 nM to 5 microM) and reduced the sHVA current at high concentrations (>10 microM). The GABA-mediated enhancement of the Ca2+ current at low concentrations was sensitive to block by picrotoxin. The protein kinase A (PKA) inhibitor peptide [PKI(6-22)amide] blocked enhancement of both Ca2+ currents produced by cAMP analogs and GABA, suggesting that the effects at low concentrations may be PKA mediated. Caged GTP-gamma-S released by flash photolysis reduced the sHVA current, and pretreatment of the photoreceptors with pertussis toxin blocked the effects of higher concentrations of GABA, indicating that at higher concentrations, the effects may be G-protein mediated.

Animals↗

PubMed1996

Time-dependent increase in protein phosphorylation following one-trial enhancement in Hermissenda.

One-trial conditioning of the nudibranch mollusk Hermissenda produces short- and long-term changes in excitability (enhancement) of identified sensory neurons. To investigate the biochemical mechanisms underlying this example of plasticity, we have examined changes in protein phosphorylation at different times following the in vitro conditioning trial. Changes in the incorporation of 32 PO4 into proteins were determined using two-dimensional polyacrylamide gel electrophoresis, autoradiography, and densitometry. Conditioning resulted in increases in levels of several phosphoproteins, five of which, ranging in apparent molecular mass from 22 to 55 kDa, were chosen for analysis. The increased phosphorylation of the 46- and 55-kDa phosphoproteins, detected 2 h postconditioning was significantly greater than the level of phosphorylation detected in an unpaired control group, indicating that long-term enhancement is pairing specific. Statistically significant increases in phosphorylation as compared with the control group that received only light were detected immediately after conditioning (5 min) for the 55-, 46-, and 22-kDa phosphoproteins, at 1 h for the 55- and 46-kDa phosphoproteins, and at 2 h for the 55-, 46-, and 22-kDa phosphoproteins. The 46- and 55-kDa phosphoproteins are putative structural proteins, and the 22-kDa phosphoprotein is proposed to be a protein kinase C substrate previously identified in Hermissenda following multitrial classical conditioning. Time-dependent increases in protein phosphorylation may contribute to the induction and maintenance of different memory stages expressed in sensory neurons after one-trial conditioning.

Animals↗

PubMed1995

Consensus on minimal criteria of clinical and neuropathological diagnosis of schizophrenia and affective disorders for post mortem research. Report from the European Dementia and Schizophrenia Network (BIOMED I).

The sophisticated analysis of and growing information on the human brain requires that acquisition, dissection, storage and distribution of rare material are managed in a professional way. In this publication we present the consensus of the European work group "European Dementia and Schizophrenia Network", granted by the BIOMED I project of the EU, on minimal neuropathological and clinical requirements to include brains of patients with schizophrenia and affective disorders in post mortem studies. The description of clinical prerequisites in different EU countries and institutions is followed by a consensus on tissue handling, a consensus on minimal neuropathological criteria and a consensus on minimal clinical diagnostic criteria including clinical vignette, family, social, education/professional and general medical histories, general physical history including neurostatus, neurological, psychiatric, medication and general pathological histories, psychostatus, laboratory tests and a history provided by family/health care giver questionnaire. This publication should give help to interconnect different European brain bank centers on a basis of standardized protocols.

Brain↗

PubMed1995

Evidence for a contribution of ICa to serotonergic modulation of IK,Ca in Hermissenda photoreceptors.

1. The Ca(2+)-dependent K+ current (IK,Ca) contributes to both the plateau phase of light-elicited generator potentials and enhanced excitability of identified type B photoreceptors of Hermissenda detected after classical conditioning. Serotonergic modulation of membrane conductances mimics some of the effects of conditioning. Serotonin (5-HT) reduces the magnitude of IK,Ca and decreases the sustained voltage-activated Ca2+ current (ICa) in type B photoreceptors. We have examined the modulatory role of 5-HT in regulation of IK,Ca by ICa using a Ca2+ ionophore in conjunction with the whole cell patch-clamp technique in isolated photoreceptors. 2. The 40-50% reduction of IK,Ca by 5-HT was voltage independent. Cd2+ blocked ICa and reduced IK,Ca by 70-80%. The remaining 20-30% of IK,Ca may result from Ca2+ release from intracellular stores, because IK,Ca was further reduced to 5-10% as the pipette ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) was raised from 0.5 to 5 mM. The application of the Ca2+ ionophore A23187, which was designed to produce Ca2+ influx independent of the voltage-activated Ca2+ channels, restored IK,Ca. 3. The application of A23187 reversed the effects of 5-HT and Cd2+ on IK,Ca for experiments lasting 15-20 min. However, for longer time periods (> 25 min), complete restoration of IK,Ca by A23187 was obtained in the presence of Cd2+ but not 5-HT. These results suggest that for 15 to 20 min exposures the reduction of IK,Ca by 5-HT is a consequence of modulation of ICa by 5-HT and not a direct effect of 5-HT on IK,Ca.

Animals↗

PubMed1995

Characterization of voltage-activated currents in Hermissenda type B-photoreceptors.

Two distinct voltage-dependent K+ currents have been previously identified in the type B-photoreceptors of Hermissenda: an early, rapidly inactivating K+ current (IA), and a late, 4-AP- and TEA-resistant voltage and Ca(2+)-dependent current (IK(Ca)). Using conventional two-electrode voltage-clamp techniques, we have characterized two additional currents, a late voltage-dependent outward K+ current (IK(v)) and a voltage-dependent inward current identified as an inward rectifier (Iir). In addition, we have further studied the activation-inactivation kinetics of IA. In 0-Na+ ASW, Iir activates at a potential of > -50 mV, is steeply voltage-dependent and noninactivating, and reaches steady-state within 800 msec to 3 sec at -100 mV. In addition to the variability in activation kinetics, there was also considerable variability in Iir magnitude (-5 to -80 nA, at -100 mV). Iir was blocked by external 4-AP (5 mM), external and internal TEA, internal Cs+, but not external Ba2+. The major component of outward K+ current in type B-photoreceptors is IK(v), the delayed rectifier. IK(v) was isolated after removal of IA and IK(Ca). IK(v) activates at around -25 mV or more positive membrane potentials and its activation and inactivation are strongly voltage dependent. IK(v) inactivation to steady state is reached within 1.5-2.5 sec. The wide range of activation-inactivation rates suggests that there may be kinetic subtypes of IK(v). The proposed "slow" IK(v) peaked in 50-90 msec at +30 mV, and decayed with a single exponential component with an average tau off of 279 msec. Proposed "intermediate" and "fast" IK(v) subtypes peaked within 12-50 msec at +30 mV, and had a decay fitted by two exponentials, with an average tau 1 of 147 msec and tau 2 of 275 msec, respectively. IK(v) exhibited marked twin-pulse inactivation with a recovery time of 30-40 sec, and also exhibited time- and voltage-dependent cumulative inactivation to repeated depolarizing pulses. Both types of inactivation were quickly removed by a prepulse hyperpolarization. 4-AP (5 mM) produced partial to complete block of the inactivating component of IK(v), leaving only a residual sustained component. Complete block of the transient and sustained components of IK(v) was obtained by 100 mM TEA. Reliable voltage separation of IA from IK(v) was achieved by activating IA in the range of -50 to -20 mV, from a Vh of -80 mV. Voltage-dependent steady-state inactivation curves for IA were determined, yielding an average h0.5 value of -56 mV.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Aminopyridine↗

PubMed1994

Linkage analysis between schizophrenia and a microsatellite polymorphism for the D5 dopamine receptor gene.

Using 23 multiplex pedigrees we tested for linkage between schizophrenia and a microsatellite polymorphism for the D5 dopamine receptor gene (DRD5). Assuming autosomal dominant inheritance and a maximum penetrance of 0.6, an overall lod score of -4.54 was derived at 0% recombination. For recessive transmission the summary lod score was -8.37 at 0% recombination. These data suggest that mutations of the D5 dopamine receptor gene are unlikely to be of major etiological importance in the pathogeneses of schizophrenia in the families studied. However, our study does not exclude the D5 dopamine receptor gene as a candidate gene for schizophrenia because some of our families were not informative for linkage and because of the likelihood of genetic heterogeneity.

Adolescent↗

PubMed1994

Two components of calcium currents in the soma of photoreceptors of Hermissenda.

1. The proposed mechanism of cellular plasticity underlying classical conditioning of Hermissenda involves Ca2+ influx through voltage-activated channels. This influx triggers several molecular cascades and leads to the phosphorylation of K+ channels in identified photoreceptors. We studied Ca2+ currents from isolated photoreceptors of Hermissenda with the whole cell patch-clamp technique. Two distinct Ca2+ currents were identified in isolated photoreceptors on the basis of differences in their voltage dependence, kinetics, and pharmacology. 2. One Ca2+ current was transient (ICa(t)), with a fast onset (approximately 5 ms), activated at -50 mV from a holding potential of -90 mV, and peaked at 0 mV. The second Ca2+ current, designated as sustained (ICa(s)), exhibited a delayed time-to-peak, activated at -30 mV, and reached maximum at 30 mV. 3. Steady-state activation curves for both currents were generated from normalized currents and fitted with the Boltzmann function; estimates of half-activation voltages for ICa(t) were -38.8 +/- 6.7 mV (mean +/- SD; n = 9) and 3.2 +/- 8.2 mV for ICa(s) (n = 11) with maximum slopes of 8.9 +/- 1.6 mV (n = 9) and 11.0 +/- 2.4 mV (n = 11). 4. The inactivation of ICa(s) was slow (time constants > 3 s) whereas ICa(t) inactivated rapidly (time constant of inactivation at various voltages; 75-600 ms). 5. Ni2+ (0.8 mM), Gd3+ (0.5 mM), and amiloride (10 microM) produced a reversible block of ICa(t) without affecting ICa(s). omega-Conotoxin GVIA (10 nM) irreversibly blocked ICa(s) whereas nitrendipine (20 microM) produced a reversible block. 6. ICa(t) may be responsible for steady-state membrane potential oscillations. ICa(s) may contribute to the maintenance of the amplitude of the plateau phase of the generator potential.

Animals↗