ISSN:
1432-1351
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary 1. The membrane current underlying the hyperpolarizing receptor response following a mechanical stimulus to the cell posterior of the hypotriche ciliateStylonychia mytilus was investigated with a two microelectrode voltage-clamp technique. 2. The relationship between the amplitude and the time course of the receptor current and the wave form of the voltage pulse driving the mechanical stimulation system was studied (Figs. 2, 3, 4). The amplitude of the receptor current increased approximately linearly with the driving pulse, but both amplitude and time course of the receptor current were unaffected by varying the duration of the driving pulse. 3. The mean maximum amplitude of the receptor current elicited by mechanical stimuli was 20.4 ± 5.6 nA (± S.D., n=19) at the normal resting potential of −51.4±1.6 mV (n=20). This corresponds to an averagemaximum conductance increase of 0.61 μS. The receptor current flow reversed its direction at a membrane potential of −87.7±3.3 mV (n=18; Figs. 5, 6). At the extracellular K+ concentration of 1 mM, the intracellular K+ concentration was calculated to be 33.3 mM. 4. The amplitude of the receptor current changed linearly with the membrane potential in the hyperpolarizing direction. In the depolarizing direction the receptor current amplitude increased less than expected from the increased driving force. The conductance increase following a mechanical stimulus was in average less than 50% at zero mV as compared with that at the normal resting potential of around −50 mV. 5. The receptor current decayed with a single exponential time course, its mean time constant was 7.3±1.2 ms (n=15). The time course of the receptor current changed with the membrane voltage. The rise time and the time constant of decay of the receptor current increased with hyperpolarization towards the reversal potential, and both decreased with depolarization (Figs. 7, 8). These changes with membrane potential were approximately exponential; the voltage displacement to achieve an e-fold increase of the rise time was −410 mV, and of the decay time constant −110 mV. At membrane potentials just beyond the reversal potential both rise time and decay time constant of the receptor current, now flowinginward, were reduced by 20 to 50%, before increasing again with further hyperpolarization (Fig. 9). 6. The results indicate that the life time and possibly the conductance of mechanically activated ionic channels are dependent on the membrane voltage. The implications of these findings for a mechanoreceptor are compared with data obtained at chemoreceptors, e.g. at neuromuscular junctions and other chemical synapses.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01342664
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