The excitatory glutamate-activated channel recorded in cell-attached and excised patches from the membranes of tail, leg and stomach muscles of crayfish

Abstract

Glutamate activated, excitatory single channel currents were recorded from 5 different muscles of crayfish (Austropotamobius torrentium) from abdomen, legs and stomach. Cell-attached and outside-out excised membrane patches with GΩ-seals were studied. At −70 mV membrane potential and 19 °C, single channel currents activated by 0.5 mM glutamate had an amplitude of −7.6 pA, a mean open time of 0.22 ms and a mean burst length of 0.58 ms. These values did not show significant differences in all muscles investigated. The distributions of open times and of burst durations were described by single exponentials. The distributions of closed times could be fitted only by at least two exponentials. The short component of on average 0.1 ms represented closings within bursts, a longer component of on average 0.9 ms grouping of bursts. Burst durations (but not individual open times) increased with rising glutamate concentration: the relative open time of the channel was approximately proportional to glutamate concentration between 0.1 and 5 mM. The channels described above could not be activated by the glutamate analogues kainate and NMDA, but were about 10 times more sensitive to quisqualate than to glutamate. Quisqualate elicited single channel currents of the same amplitude as those triggered by glutamate. Compared at the same concentrations, channel open times and burst durations were about 4 times longer in quisqualate than in glutamate. A model describing the kinetics of the glutamate-activated excitatory channels is discussed. In addition, a type of Ca-independent, depolarization-activated K+-channel is reported.