Ion (H+, Ca2+, Co2+) and temperature effects on a hyperpolarization-activated membrane current in the lobster stretch receptor neurone.
The effects of some ions (H+, Ca2+, Co2+) and temperature on the Q-channel (a channel which conducts a hyperpolarization-activated membrane current, IQ) was investigated in the slowly adapting lobster stretch receptor neurone. It was found: (1) that increases in pH cause an increase in the maximum channel conductance; (2) that Co2+ (1 mM) and increases in extracellular Ca2+ produce a positive shift of the relationship between the membrane voltage and the steady-state channel activation along the voltage scale; (3) that Co2+ and decreases in extracellular pH cause a decrease in rate of the voltage-dependent step of the channel's gating reaction; (4) that none of the ions has an effect on the rate of the voltage-independent step of the gating reaction; and (5) that Co2+ and K+ do not interfere with each other's actions on the channel's gating reaction and maximum ion conductivity. Increases in temperature from 13 to 23 degrees C were found: (1) to cause an increase in the maximum Q-channel conductance by a factor of 1.7; (2) to have no effect on the voltage dependence of the channel's gating reaction; but (3) to lead to an increase in rate of the gating reaction by a factor of about five for the voltage-dependent, and by a factor of about three for the voltage-independent gating step. The temperature sensitivity of the IQ mechanism proved to be mathematically reproducible by a previously developed, and slightly modified Q-channel model (Edman et al. 1987, Edman & Grampp 1989), and to be of no significance in the control of membrane excitability in a thermally unstable environment.
Edman
A
A
Department of Physiology and Biophysics, University of Lund, Sweden.
Grampp
W
W
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D003035:Cobalt / Q000494:pharmacology*; D004553:Electric Conductivity / Q000187:drug effects / Q000502:physiology; D006859:Hydrogen / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating; D008465:Mechanoreceptors / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008121:Nephropidae / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D013696:Temperature
D003035:Cobalt; D006859:Hydrogen; D011188:Potassium; D002118:Calcium