QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

Help viewing high resolution images Return to article

Fig. 4. Action potentials in muscle fibres from honeybee. (A) Three superimposed current steps of 10 ms duration and of increasing amplitude (i) and membrane voltage responses (ii) in a current-clamped muscle fibre bathed in Tyrode's solution (2 mmol l^–1 CaCl₂). The membrane potential was held at –80 mV by passing a constant negative current (minus sign at the beginning of the voltage recordings). Both of the lowest stimulating current steps (a, thin traces) only elicited electrotonic responses. The highest current amplitude (i, thick trace) elicited an action potential overshooting 0 mV (broken line marks the 0 mV level). (B) Three superimposed current steps of 1000 ms duration and of increasing amplitude (i) and the three corresponding membrane voltage responses from bottom to top (ii) in another current-clamped muscle fibre bathed in Tyrode's solution. The membrane potential was held at –80 mV by passing a constant negative current. Whereas the first current step only elicited an electrotonus (ii, bottom trace), the intermediate current step triggered a single action potential (ii, middle trace). The highest current step triggered a train of action potentials (ii, upper trace). (C) In current-clamp, tetrodotoxin (TTX) had no effect on the action potential (upper panel) whereas the calcium channel blockers Cd²⁺ and La³⁺ converted the regenerative action potential response (black line, lower panel) into an electrotonic response (broken line). E_m, voltage command.

Return to article