Abstract
Toxin isolated from nematocysts of the sea nettle Chrysaora quinquecirrha (SNTX) is known to depolarize nerve and muscle membranes and to increase the miniature end-plate potentials' frequency. To investigate its mode of action at the membrane level, we have studied the toxin's effects on the frog myelinated nerve fibre. We show that SNTX creates large cation-selective channels that open and close spontaneously. The conductance of these channels, almost constant in the voltage range - 100 to + 50 mV, is 760 pS. The SNTX-induced channels are almost equally permeable to Na+, Li+, K+, and Cs+, but are impermeable to Ca++. The open and closed times of SNTX-induced channels are voltage dependent, the open probability increasing with increased negative membrane potentials. To our knowledge, this is the first demonstration of the production of single-channel currents by a toxin, in a biological membrane.
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