The effects of pH and drugs on miniature end plate current decay in extraocular muscles of the Antarctic fish Pagothenia borchgrevinki

Previous experiments indicated that miniature end plate currents (MEPCs) from extraocular muscles of Antarctic fish decay significantly faster than MEPCs from New Zealand temperate fish. As the Antarctic fish contains higher proportion of unsaturated fluid lipids, the fast MEPC decay agrees with the hypothesis relating membrane channel kinetics to membrane viscosity. Recordings of spontaneous MEPCs were made from extraocular muscles of Pagothenia borchgrevinki in order to test the effects of several interacting variables. The effects of pH and drugs on MEPC decay were assessed. MEPCs were recorded in pH 6.55, 7.55 and 8.55 and three drugs were used to test the effects of abundance of neuromuscular transmitter molecules and transmitter sensitive sites and how they may affect the shape of MEPCs. The three drugs were Neostigmine: a cholinesterase inhibitor which would block the inhibitor, Tubocurarine: a receptor blocker which would reduce the number of active receptor sites and Deuterium oxide. The number of quantal doses of acetylcholine released by a nerve to activate a muscle can be estimated by recording repeated responses (end plate potentials (EPPs) to nerve stimulation and calculating mean EPP amplitude and variance. Evoked EPPS were recorded over a range of temperatures (-2°C to 12°C) and was used to estimate the quantal content.