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M B Goodman

Publications and source records attributed to M B Goodman.

12 recordsLinked to original sources
PubMed1998

Active currents regulate sensitivity and dynamic range in C. elegans neurons.

Little is known about the physiology of neurons in Caenorhabditis elegans. Using new techniques for in situ patch-clamp recording in C. elegans, we analyzed the electrical properties of an identified sensory neuron (ASER) across four developmental stages and 42 unidentified neurons at one stage. We find that ASER is nearly isopotential and fails to generate classical Na+ action potentials. Rather, ASER displays a high sensitivity to input currents coupled to a depolarization-dependent reduction in sensitivity that may endow ASER with a wide dynamic range. Voltage clamp revealed depolarization-activated K+ and Ca2+ currents that contribute to high sensitivity near the zero-current potential. The depolarization-dependent reduction in sensitivity can be attributed to activation of K+ current at voltages where it dominates the net membrane current. The voltage dependence of membrane current was similar in all neurons examined, suggesting that C. elegans neurons share a common mechanism of sensitivity and dynamic range.

Animals↗
PubMed1996

Variations in the ensemble of potassium currents underlying resonance in turtle hair cells.

1. Potassium currents were characterized in turtle cochlear hair cells by whole-cell voltage clamp during superfusion with the potassium channel antagonists, tetraethylammonium (TEA) and 4-aminopyridine (4-AP). The estimated resonant frequency, f0, was inferred from tau, the time constant of deactivation of outward current upon repolarization to -50 mV, according to the empirical relation, f0 = k1 tau-1/2 + k2. 2. Dose-response relations for TEA and 4-AP were obtained by exposing single cells to ten concentrations exponentially distributed over four orders of magnitude. Potassium current in cells tuned to low frequencies was carried by a single class of channels with an apparent affinity constant, K1, for TEA of 35.9 mM. Half-blocking concentrations of 4-AP were correlated with the time constant of deactivation and varied between 26.2 and 102 microM. In cells tuned to higher frequencies, K+ current was carried by a single class of channels with high affinity for TEA (K1 = 0.215 mM) and low affinity for 4-AP (K1 = 12.3 mM). This pharmacological profile suggests that K+ current in low frequency cells is purely voltage gated and in high frequency cells, it is gated by both Ca2+ and voltage. 3. For each current type, the voltage dependence of activation was determined from tail current amplitude at -50 mV. The purely voltage-gated current, IK(V), was found to increase e-fold in 4.0 +/- 0.3 mV (n = 3) in low frequency cells exposed to TEA (25 mM). The Ca(2+)- and voltage-gated current, IK(Ca), was more steeply voltage dependent, increasing e-fold in 1.9 mV (n = 2) in high frequency cells exposed to 4-AP (0.8 mM). 4. IK(V) was found to inactivate slowly during prolonged voltage steps (approximately 10 s). Steady-state inactivation increased with depolarization from -70 mV and was incomplete such that on average IK(v) did not fall below approximately 0.39 of its maximum value. 5. Superfusion of 4-AP (0.8 mM) reversibly depolarized a low frequency cell and eliminated steady voltage oscillations, while TEA (6 mM) had no effect. In a high frequency cell, voltage oscillations were abolished by TEA, but not by 4-AP. 6. The differential pharmacology of IK(V) and IK(Ca) was used to measure their contribution to K+ current in cells tuned to different frequencies. Both currents exhibited a frequency-dependent increase in maximum conductance. IK(V) accounted for nearly all K+ current in cells tuned to less than 60 Hz, while IK(Ca) was the dominant current in higher frequency cells. 7. Mapping resonant frequency onto epithelial position suggests an exponential relation between K+ current size and position. IK(V) appeared to be limited to the apical or low frequency portion of the basilar papilla and coincided with maximal expression of a K(+)-selective inward rectifier, IK(IR). This finding is consistent with the notion that low frequency resonance is produced by interaction of IK(V) and IK(IR) with the voltage-gated Ca2+ current, ICa, and the cell's capacitance. The ionic events underlying higher frequency resonance are dominated by the action of IK(Ca) and ICa and include a contribution from IK(IR).

4-Aminopyridine↗
PubMed1996

Positive feedback by a potassium-selective inward rectifier enhances tuning in vertebrate hair cells.

Electrical resonance in vertebrate hair cells shapes receptor potentials and tunes each cell to a narrow band of frequencies. We have investigated the contribution of a potassium-selective inward rectifier (IR) to electrical resonance, isolating outward current carried by IR from other ionic currents active in the physiological voltage range (-75 to -30 mV) using a combination of potassium and calcium channel antagonists. IR expression is tightly regulated in the turtle's auditory epithelium, as revealed by the observation that its size declines systematically with resonant frequency. A critical feature of IR is the rapid inhibition produced by depolarization, which results in a negative slope in the steady-state current-voltage relation in the vicinity of the resting potential (-50 mV). The increasing block of outward current produced by depolarization is functionally equivalent to activating an inward current, suggesting that IR provides positive feedback and, in hair cells, serves an electrical function ordinarily reserved for voltage-dependent sodium and calcium currents. Additional support for this idea comes from the observation that superfusion with cesium selectively reduces IR and eliminates resonance in cells tuned to low frequencies and degrades resonant quality in cells tuned to more than 50 Hz.

Animals↗
PubMed1991

Activation of the inositol trisphosphate second messenger system by cAMP in a mouse fibroblast cell line.

Intracellular Ca2+ mobilization events were assessed in mouse L cells, which contain native prostaglandin E1 receptors and transfected human beta 2 adrenergic receptors. Both Fura2 (single cell measurements) and Quin 2, (cuvette assays) were used to determine [Ca2+]i levels. Our results demonstrate that in the transfected cells there is a dose-dependent increase in [Ca2+]i in response to isoproterenol (0.1 nM-100 nM), which is inhibited by the beta-adrenergic antagonist, propranolol, and is a result of intracellular Ca2+ release. [Ca2+]i in these cells was also increased by prostaglandin E1, 8 bromo cyclic AMP, and aluminum fluoride. Both 8 bromo cAMP and isoproterenol induced a rapid increase in the levels of IP1, IP2, and IP3. The data presented demonstrate that the elevation of intracellular cyclic AMP induces an increase in IP3 production which leads to an elevation in [Ca2+]i. We propose that this cyclic AMP dependent activation of the IP3 generating system occurs at a post-receptor site.

Animals↗
PubMed1990

Inositol trisphosphate mediates cloned muscarinic receptor-activated conductances in transfected mouse fibroblast A9 L cells.

1. The mechanism by which cloned m1 and m3 muscarinic receptor subtypes activate Ca2+-dependent channels was investigated with whole-cell and cell-attached patch-clamp recording techniques and with Fura-2 Ca2+ indicator dye measurements in cultured A9 L cells transfected with rat m1 and m3 cDNAs. 2. The Ca2+-dependent K+ and Cl- currents induced by muscarinic receptor stimulation were dependent on GTP. Responses were reduced when GTP was excluded from the intracellular recording solution or when GDP-beta-S was added. Intracellular GTP-gamma-S activated spontaneous fluctuations and permitted only one acetylcholine-(ACh) induced current response. These results implicate GTP-binding proteins (G protein) in the signal transduction pathway. This G protein is probably not pertussis toxin-sensitive as the ACh-induced electrical response was not abolished by pertussis toxin treatment. 3. Cell-attached single-channel recordings revealed activation of ion channels within the patch during application of ACh outside the patch, implying that second messengers might be involved in the ACh-induced response. Two types of K+ channel were activated, a discrete channel of 36 pS and channel activity calculated to be about 5 pS. 4. Application of 8-bromo cyclic AMP or 1-oleoyl-1,2-acetylglycerol (OAG) produced no electrical response and did not affect the ACh-induced responses. Phorbol myristic acetate (PMA) evoked no electrical response, but reduced the ACh-induced responses. 5. Inclusion of inositol 1,4,5-trisphosphate (IP3) in the intracellular pipette solution activated outward currents at -50 mV associated with an increase in conductance. The IP3-induced current response reversed polarity at -65 mV and showed a dependence on K+. Increasing the intracellular free Ca2+ concentration ([Ca2+]i) from 20 nM to 1 microM also induced an outward current response associated with an increase in conductance. Inclusion of inositol 1,3,4,5-tetrakisphosphate (IP4) in the intracellular solution had no effect on the A9 L cells. 6. Fura-2 measurements revealed ACh-induced increases in Cai2+. The Ca2+ responses were abolished by atropine showing that they were muscarinic in nature. Removal of extracellular Ca2+ did not affect the initial ACh-induced increase in Cai2+ but subsequent Cai2+ responses to ACh were depressed, suggesting depletion of Ca2+ intracellular stores. Residual though small responses continued to be elicited by ACh. Barium (5 mM) had little effect and cobalt slightly reduced the ACh-induced Ca2+ response. 7. The ACh-induced currents recorded at -50 mV were unaffected by removal of extracellular Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗
PubMed1988

Calcium currents and fura-2 signals in fluorescence-activated cell sorted lactotrophs and somatotrophs of rat anterior pituitary.

Optical and electrical recording techniques were applied to single primary pituitary cells to characterize the types of voltage-dependent calcium currents (ICa) and levels of intracellular calcium ([Ca2+]i). GH-containing somatotrophs and PRL-containing lactotrophs were isolated from adult female rats using fluorescence-activated cell-sorting techniques and were maintained in culture for 1-4 days. Whole cell patch-clamp recordings were made to analyze the ICa, and [Ca2+]i was measured with fura-2. Cell type was verified after each recording by indirect immunocytochemistry. GH and PRL cells could be divided into two groups: silent and spontaneously active. Silent cells had stable membrane potentials and stable levels of [Ca2+]i. Spontaneously active cells exhibited spontaneous action potentials and large fluctuations in [Ca2+]i. Two types of ICa were found: a low threshold, transient current which was insensitive to the dihydropyridine -Bay 5417 (the negative isomer of Bay K 8644), and a high threshold, sustained current which was enhanced by -Bay 5417. Both types of ICa were present in PRL and GH cells, but each cell type differed quantitatively in the proportion of each current type. While the GH cells had a more prominent, low threshold, transient ICa, the PRL cells had a more prominent, high threshold, sustained ICa. The enhancement of ICa by -Bay 5417 was greater in the PRL cells, which have a larger dihydropyridine-sensitive ICa. Parallel fura-2 measurements showed an increase in [Ca2+]i in response to 50 mM KCl and -Bay 5417 for both lactotrophs and somatotrophs.

Animals↗