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Biomedical subjects

S F Fan

Publications and source records attributed to S F Fan.

At least 19 recordsLinked to original sources
PubMed1992

Difference in the effects of verapamil on Ca(2+)-activated K+ channels of smooth myocytes of aorta and taenia coli.

In freshly dispersed taenia coli myocytes of guinea pig, verapamil decreased the whole-cell outward current during depolarization. In aortic myocytes it has the opposite effect. In cell-attached patches, verapamil increased the frequency of opening of the maxi-K+ channel of both taenia coli and aortic myocytes at the expense of the mean open time. In taenia coli myocytes, the greater frequency did not fully compensate for the reduced open time, and the overall open probability of the channel was reduced. In aortic myocytes, the increase in open frequency overwhelmed the effect of the decrease in mean open time. None of the effects could be reproduced with nifedipine or diltiazem in either cell type.

Animals↗
PubMed1992

F11 neuroblastoma x DRG neuron hybrid cells express inhibitory mu- and delta-opioid receptors which increase voltage-dependent K+ currents upon activation.

The F11 cell line is a fusion product of cells of mouse neuroblastoma cell line N18TG-2 with embryonic rat dorsal-root ganglion (DRG) neurons. Previous biochemical results suggest that they express mu- and delta-opioid receptors that are negatively coupled to adenylate cyclase. The present study provides direct agonist-binding and electrophysiologic evidence of mu and delta, but not kappa, receptor expression in F11 cells. Radioligand binding assays show that F11 cell membranes bind the mu- and delta-opioid receptor agonists, DAGO and DPDPE with Kd = 4.5 and 4.9 nM and Bmax = 111 and 195 fmol/mg, respectively. Tight-seal patch-clamp recordings of F11 cells after several days in a differentiating culture medium (low serum, cyclic AMP and nerve growth factor) showed that: (i) the outward K+ current during pulsed depolarization in most of these cells was increased by either DAGO or DPDPE, but none were responsive to both opioids or to the kappa-opioid receptor agonist, U-50,488H. The response was blocked by relevant receptor antagonists, naloxone, beta-funaltrexamine or naltrindole; (ii) cells without processes responded neither to DAGO nor to DPDPE; (iii) treatment with pertussis toxin blocked all opioid-induced increases in outward K+ current. The opioid-induced increase in voltage-dependent membrane K+ current in F11 cells resembles the inhibitory effect elicited by mu- and delta-opioid agonists in primary cultures of mouse DRG neurons.

Animals↗
PubMed1992

Suppression of crossbridge motions of isolated thick myofilaments in ATP-free medium by thiourea.

Thiourea is known to suppress the contractile response of Mytilus anterior byssus retractor muscle and toad sartorious muscle following electrical or chemical stimulation without abolishing of the electrical responses. In addition, it blocks the shortening of glycerinated sartorious muscle induced by Ca2+. With dynamic laser light scattering method we found that thiourea suppresses the increase of the average linewidth of the photoelectron count autocorrelation function, gamma, of isolated thick filaments of Limulus striated muscle induced by depletion of ATP. The results obtained suggest that thiourea prevents the crossbridges from moving away from the thick myofilament backbones which will, in turn, prohibit the crossbridges from interacting with the thin myofilaments.

Adenosine Triphosphate↗
PubMed1992

Seasonal changes in the activation of crossbridge motions of isolated thick filament from Limulus striated muscle.

In dynamic light scattering, measurements of the intensity-intensity time correlation function from a suspension of rod-like particles of length L could reveal dynamical information related to translational and internal motions of those particles. For a suspension of thick filaments isolated from the myosin-regulated, striated muscles of Limulus at KL greater than 1 (where K is the scattering vector), the average characteristic linewidth (gamma) increased with the addition of Ca2+ or with the depletion of ATP. The increase in the gamma with the addition of Ca2+ could be due to the presence of energy-requiring, high-frequency motions of the crossbridges activated by Ca2+. The increase in gamma which occurred with the depletion of ATP was assumed to be mainly due to the thermal motions of the crossbridges after they had moved radially away from the filament backbone. The percentage increase in gamma following the addition of Ca2+ was found to be seasonal, i.e., values of gamma obtained from thick filaments isolated between the middle of June and the middle of September were smaller than those obtained during the rest of the year. The effect of temperature on the percentage increase in gamma was also different. The increase showed a maximum at about 35 degrees C during the summer and at about 25 degrees C at other times. However, the percentage increase in gamma developed under ATP-depleted conditions showed no temperature-related maximum. The number of bound Ca2+ per myosin molecule was 1 during the summer and 2 at other times.

Adenosine Triphosphate↗
PubMed1992

Model invariant method for extracting single-channel mean open and closed times from heterogeneous multichannel records.

We present a proof that the mean open (and closed) times of the individual channels in a multichannel record can be found in a model-independent fashion. As the results are model independent, they can be derived by assuming the simplest model for all the channels, namely that they all have the basic CLOSED in equilibrium with OPEN scheme. In particular, the method can be applied to patches where the channel population is heterogenous with respect to open probability. Multichannel simulations are performed to test the limits of applicability of this method to restricted amounts of data. One conclusion is that increasing the number of channels does not substantially reduce the errors in estimating the mean times, in spite of the 'increased information' present. We also prove the general applicability of the algorithm of Fenwick et al. (1982) in estimating the mean times without knowledge of the number of channels present, and discuss its limitations. An illustration using experimental data is also given.

Algorithms↗
PubMed1991

Opioids at low concentration decrease openings of K+ channels in sensory ganglion neurons.

Previous studies showed that low concentrations of opioids prolong the calcium-dependent component of the action potential duration (APD) of dorsal root ganglion (DRG) neurons, whereas higher concentrations shorten the APD. In the present study whole-cell voltage-clamp, as well as cell-attached membrane-patch voltage-clamp, recordings demonstrate that application of picomolar to nanomolar concentrations of mu, delta or kappa opioid agonists (DAGO, DPDPE or dynorphin) to DRG neurons in dissociated cell cultures reversibly decreased the activities of voltage-sensitive K+ channels. Pretreatment of DRG neurons with the opioid receptor antagonists, naloxone (30 nM) or diprenorphine (1 nM) prevented mu/delta or kappa opioid-induced decreases in K+ channel activities, respectively. Since opioids added to the bath solution decreased the activities of K+ channels in the membrane patch sealed off by the pipette tip, our results provide strong evidence that some modes of excitatory modulation of the action potential of DRG neurons are mediated by diffusible second messengers. The data are consonant with our previous studies indicating that opioids can elicit excitatory effects on sensory neurons via cholera toxin-sensitive Gs-linked excitatory opioid receptors coupled to cyclic AMP-dependent ionic channels.

Action Potentials↗
PubMed1989

Patch clamp recordings from membranes which contain gap junction channels.

The septal membranes of the median and lateral giant axons of earthworm, which contain gap junctions, were exposed by cutting one segment of the cord. Patch recordings were obtained from the exposed cytoplasmic side of the septum. Seal resistances ranged from 2 to 15 G omega. The patch could be excised (detached) or left attached to the whole cell. Two types of channels were observed. One type was blocked by tetraethylammonium (TEA) or Cs+ and had a unitary conductance of 30-40 pS. It appears to be a K+ channel. The other channel type had a unitary conductance of 90-110 pS and was unaffected by TEA+ or Cs+. In the detached configuration the channel was shown to conduct Cs+, K+, Na+, TMA+, Cl- and TEA+ even in the presence of 2 mM Zn2+, 1 mM Ni2+, 1 mM Co2+, and 4 mM 4-aminopyridine. The conductance ratios relative to K+ were 1.0 for Cs+, 0.84 for Na+, 0.64 for TMA+, 0.52 for Cl- and 0.2 for TEA+. The channel appears to be voltage insensitive whether monitored in detached or attached recording mode. Both H+ and Ca2+ reduce the probability of opening. Thus, the 100 pS channel has many of the properties expected of a gap junction channel.

Animals↗
PubMed1987

Effect of ATP depletion on the isolated thick filament of limulus striated muscle.

With the dynamic light scattering method, we have shown that calcium ions increase the high-frequency internal motions of isolated thick filaments of Limulus striated muscle in the presence of ATP (Kubota, K., B. Chu, Shih-fang Fan, M.M. Dewey, P. Brink, and D. Colflesh. J. Mol. Biol. 1983. 166:329 and Fan, S.-f., M.M. Dewey, D. Colflesh, B. Gaylinn, R. Greguski, and B. Chu. Biophys. J. 1985. 47:809). If ATP is removed from the suspending medium, an increase of high-frequency internal motions also has been observed with characteristics different from those of filaments suspended in a medium containing ATP and calcium ions. These internal motions appear whether calcium ions are present or not and are suppressed by trifluoperazine (TFP). The motions differ from the calcium ion-induced motions in that (a) an energy supply is not required; (b) they are insensitive to heat treatment (42 degrees C, 10 min) and (c) they are also insensitive to phenylmethylsulfonyl fluoride which blocks the motions in the presence of ATP and calcium ions (Fan, Shih-fang, M.M. Dewey, D. Colflesh, B. Gaylinn, R. Greguski, and B. Chu. 1985. Biochim. Biophys. Acta. 827:101). Electron micrographs of negatively stained thick filaments in an ATP-free medium show that the majority of crossbridges extend out from the backbone of the filament and optical diffraction patterns from these filaments lack layer lines arising from the crossbridges. The flexibility of the thick filaments suspended in ATP-free media increases.

Adenosine Triphosphate↗
PubMed1985

Suppression of active cross-bridge motions of isolated thick myofilaments in suspension by phenylmethylsulfonyl fluoride.

Studies of photoelectron count autocorrelation function of light scattered from suspensions of thick filaments of Limulus telson muscle and scallop striated adductor muscle reveal that Ca2+ can activate cross-bridge motions of these isolated filaments. By treating suspensions of activated filaments with phenylmethylsulfonyl fluoride (PMSF), we can suppress active cross-bridge motions but not affect the Ca2+-dependent ATPase activity.

Adenosine Triphosphatases↗
PubMed1985

Familial osteosarcoma associated with 13;14 chromosomal rearrangement.

Two prepubertal sisters of American Indian origin developed osteosarcoma at 8 and 12 years of age. This familial occurrence, tumor onset prior to puberty, unusual tumor location in one who also had short stature, and ethnic background all suggest an inborn predisposition to bone cancer rather than a chance occurrence. Rearrangements involving chromosomes #13 and #14 were found in both the surviving proband and mother. Comparison of the arm ratio and prometaphase G-banding patterns of the rearranged chromosomes suggests either deletion of band 14q11.2 or pericentric inversion (with breakpoints at 13q12 and 14q11.2) in the proband's rearranged chromosome, but not in her mother's. Her mother, who had no malignancy, had a typical Robertsonian translocation [t(13;14)(p11;q11)]. Three previously reported children with chromosomal abnormalities developed osteosarcoma at unusually young ages, younger even than in reported sibships with osteosarcoma. The most frequently detected cytogenetic abnormalities in sarcoma tumor cells involve chromosomes #13 and #14. In addition, some cases of bilateral retinoblastoma and familial unilateral retinoblastoma, which are known to be at increased risk for osteosarcoma, are associated with tiny deletions on chromosome #13. Thus, there may be a causal relationship between constitutional loss or rearrangement of genetic material at these breakpoints on chromosomes #13 or #14 and development of osteosarcoma in this family that is similar to that seen in patients with small constitutional chromosomal deletions who develop Wilms' tumor and retinoblastoma.

Adolescent↗
PubMed1985

The active cross-bridge motions of isolated thick filaments from myosin-regulated muscles detected by quasi-elastic light scattering.

Intensity fluctuation spectroscopy has been used successfully as a probe that can detect an increase in high-frequency internal motions of isolated thick filaments of Limulus muscle upon the addition of calcium ions. We have attributed such motions to cross-bridge motion instead of to an increase in the flexibility of the filament backbone. Here we show that after cleavage of the S-1 and then the S-2 moieties with papain, cross-linking the myosin heads to the filament backbone, or heat denaturation (42 degrees C, 10 min), the increase in the high frequency internal motions in the thick filaments no longer occurs. Congo Red, which has been shown to induce shortening of isolated myofibrils, also increases the high-frequency motions of the isolated filaments. Furthermore, the increase is suppressed by treating the filaments with a myosin ATPase inhibitor such as vanadate ions (10 mM) or by replacing ATP with either an equimolar CrADP or the nonhydrolyzable ATP analogue beta, gamma-imido-adenine-5'-triphosphate (AMP-PNP). Calcium ions have a similar effect on isolated thick filaments from scallop muscle, where the myosin is known to be regulatory. Calcium ions have no such effect on thick filaments isolated from frog muscle, which is believed not to be regulated by calcium binding to myosin. These results confirm our earlier supposition that the additional high frequency internal motions of the thick filaments isolated from striated muscle of Limulus are related to the energy dependent, active cross-bridge motions.

Adenosine Triphosphatases↗
PubMed1984

Limulus striated muscle provides an unusual model for muscle contraction.

Although nearly two decades have passed since de Villafranca (1961) described A-band shortening, controversy persists. Here we will review the data which has been amassed since de Villafranca 's description. We will conclude that A-bands and thick filaments shorten during sarcomere shortening in Limulus striated muscle. Further we will suggest that two machines operate in this muscle: a tension generating sliding filament system and a tension generating thick filament shortening system. Also we will suggest a mechanism of force generation of the filament shortening system and provide evidence for a cycling bridge mechanism for this muscle.

Animals↗
PubMed1984

Dynamic laser light scattering of papain-treated thick filaments from limulus striated muscle in suspension.

Using quasielastic light scattering we have previously shown an increase in high frequency internal motion of isolated thick filament upon activation. This we have attributed to cross-bridge motion. Here we show that after cleavage of the S1 moiety of myosin from isolated filaments with papain, calcium ions no longer activate the isolated filaments to produce high-frequency motions.

Animals↗
PubMed1983

Quasi-elastic light scattering of suspensions of Limulus thick myofilaments in relaxed (long) activated and rerelaxed (short) states.

Photoelectron count autocorrelation function of light scattered by Limulus thick myofilament suspensions was measured as a function of scattering angle in the relaxed, activated and rerelaxed states. By using the cumulants method of data analysis, the average linewidth over large ranges of KL (up to 120), has been calculated with K and L being, respectively, the magnitude of the momentum transfer vector and the length of the myofilament. We have observed a dramatic increase in the average linewidth denoting the presence of additional high frequency components for the myofilament suspension on the activated state. By confirming our results on the size of the myofilaments from electron micrographs, we are able to attribute the high frequency (kHz) components to the "correlated" cross-bridge motions, representing, to our knowledge, the first direct experimental evidence of such movements in isolated thick myofilament suspensions.

Animals↗