Voltage and patch clamp studies of the ionic currents in snail neurones and frog skeletal muscle.
thesisposted on 19.11.2015, 08:44 by Thomas Anthony. Ward
The inactivation of the calcium permeability in Helix aspersa neurones was studied in relation to [Ca]. Injection of calcium ions was shown to reduce the voltage activated calcium current by increasing [Ca]. This was proved to be by a process of inactivation of the calcium current, rather than a direct effect of increased [Ca] on the driving force for calcium across the membrane. [Ca] was measured using ion sensitive electrodes, and a mean resting level of 2.66+/-0.65 x 10-7K was obtained. The inactivation of the calcium current was found to fit 1 to 1 binding between calcium and the receptor responsible for inactivation giving a Kd, of 4.8 x 10-7K. A number of techniques were used to influence the intracellular cAMP concentrations of the snail neurones in an attempt to isolate some form of metabolic control of the calcium permeability. However, no consistent responses could be obtained. The patch clamp technique was used to look at the unitary current in frog skeletal muscle. Membrane vesicles formed from the sarcolemma by enzyme treatment, were found to reduce the number of problems associated with the use of the technique on intact muscle fibres. Sodium and delayed rectifier potassium channels were identified in the vesicles, having conductances in the range 12-15pS and l6-24pS, for the two types of current. The kinetics of the sodium channels in the vesicles were found to be slightly slower than those reported for the intact frog skeletal muscle. Kowever, they could still be fitted to the m h model of Odgkin and Luxley. Studies of the kinetics of the delayed rectifier potassium channels suggested a model for the channel different from the four-closed state system proposed by odgkin and luxley. Finally, experiments were performed on snail neurons in order to observe the unitary calcium activated potassium currents.