A VOLTAGE-SENSITIVE CATION CHANNEL PRESENT IN CLUSTERS IN LOBSTER SKELETAL-MUSCLE MEMBRANE

The single channel properties of a voltage-sensitive cation channel ar e described in a study of ion channel activity in enzymatically induce d blebs of lobster skeletal muscle membrane. This cation channel, one of several that are spontaneously active in excised patches from bleb membrane, can be distinguished from other channels on the basis of its large single channel conductance (293 pS), voltage-sensitive gating p roperties, the presence of a subconductance state of the fully open ch annel, and a weak selectivity for K > Na. At hyperpolarizing voltages, this channel displays flickering or bursting behavior, and a single s tate of the fully open channel is observed. At depolarizing voltages, the mean channel open time increases and a second longer-lived open st ate is observed. The voltage dependence of the mean channel open time and the linear i-V relation of this channel predict that the macroscop ic current carried through this cation channel would be outwardly rect ifying. Channels of this type are infrequently observed in this prepar ation, but when present in the patch are often present in multiple cop ies. We describe a statistical test for examining the clustering of io n channels in excised patches of membrane. The result of this test sho ws that the cation channels appear in clusters in the blebs.