Spontaneous activity of the light-dependent channel irreversibly induced in excised patches from Limulus ventral photoreceptors |
| |
Authors: | Edwin C Johnson Juan Bacigalupo |
| |
Institution: | (1) Department of Physiology, Marshall University School of Medicine, 25755 Huntington, West Virginia;(2) Department of Biology, Faculty of Sciences, University of Chile, Santiago, Chile;(3) Present address: The Salk Institute Biotechnology Industrial Associates, Inc., 92037-4641 La Jolla, California |
| |
Abstract: | We have studied the properties of membrane patches excised from the transducing lobe of Limulus ventral photoreceptors. If patches are excised into an "internal" solution that resembles the ionic composition of the cytoplasm, channel activity is typically absent, but can be turned on by cyclic GMP (cGMP). In contrast, if patches are excised directly into sea water and subsequently examined in internal solution, they exhibit a high channel activity in the absence of any second messenger (spontaneous channel activity). Because these patches contained only light-dependent channels when examined before excision and because these spontaneous channels have properties in common with the light/cGMP-dependent channel, we believe that the spontaneously active channels represent light/cGMP-dependent channels that have been damaged by exposure to sea water, perhaps due to proteolysis activated by the high Ca2+ levels of the sea water. One type of the spontaneously active channel resembles the light/cGMP-dependent channel in open time, reversal potential, conductance states and voltage dependence. Application of micromolar Ca2+ to this channel produces a reversible decrease in the opening rate, indicating a high affinity binding site for Ca2+ on this channel. Another type of spontaneously active channel has a conductance state and reversal potential similar to the light/cGMP-dependent channel, but has apparently lost its dependence and sensitivity to Ca2+ and voltage. |
| |
Keywords: | Limulus photoreceptors ionic channels excised patches spontaneous channel activity |
本文献已被 SpringerLink 等数据库收录! |
|