Schistosoma mansoni: patch-clamp study of a nonselective cation channel in the outer tegumental membrane of females.

An apparent ion channel with a conductance of 295 pS is present in isolated inside-out patches of outer tegumental membrane taken from female Schistosoma mansoni. With positive voltages applied to the intracellular face of the patch, percentage open time for the channel was 0 to 50; with negative voltages applied, percentage open time was greater than 99. Step changes in applied voltage characteristically induced opening-closing activity. However, there was no maintained applied voltage at which there was a high level of sustained opening-closing activity. The 295 pS conductance was by far the most commonly occurring conductance but it appears to result from cooperativity among several channels, the unitary conductance for the channel averaging 95 pS. Alterations in the Na+ or K+ concentration ratios changed the reversal potential for this conductance but alterations in the Cl- concentration did not. From this it is concluded that this channel is selective for Na+ or K+ over Cl- and it appears to be a nonselective cation channel.