The permeability of the transducer membrane of the crayfish stretch receptor to calcium and other divalent cations

Abstract

The generator potential of the crayfish stretch receptor is produced by the movement of cations through a channel which is opened by stretch. Physiologically, Na + is the main ion moving through the channel; the channel is sufficiently large to admit arginine. The permeability to divalent cations has been measured in solutions in which all of the Na + was replaced by these ions. Ca 2+, Mg 2+, Sr 2+ and Ba 2+ were able to move through the channel, as shown by the membrane potential responses to stretch in solutions in which these ions were predominant. Ca 2+ (13.5 min) was found to be necessary in the Ba 2+ and Mg 2+ solutions to maintain membrane integrity; however, in the Sr 2+ solution Ca 2+ was not required. The results of voltage clamp studies showed the resting conductance to decrease in the divalent cation solutions. The reversal potential for the stretch induced current, measured with voltage clamp, was shifted in the negative direction by Ca 2+, Sr 2+ and Mg 2+. Two estimates of the value of the ratio of the permeability of Ca 2+ to that of Na +, calculated using the Goldman-Hodgkin-Katz equation, and either the change in reversal potential or the stretch induced current were 1.4 and 0.3 respectively.