Multiple conductance levels of the dihydropyridine-sensitive calcium channel in GH3 cells

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Abstract
Calcium channels in GH3 cells exhibit at least five conductance levels when examined in cell-attached or outside-out patches. These channels resemble the high threshold Ca2+ current in their range of activation and inactivation, and in their sensitivity to dihydropyridines (DHP). Mean open times for the five levels were brief (2+ and BAY K 8644, the five predominant slope conductances were 8–9, 12–13, 16–18, 23–24, and 28 pS. The present study is the first report of multiple levels of the DHP-sensitive Ca2+ channel occurring with high frequency in native membranes. The range of conductance levels that we observed encompasses the range of conductances found for two other different types of Ca2+ channels and indicates that unit conductance should be used with caution as a distinguishing characteristic for identification of different channel types.