The effects of nerve-contact, membrane excitability, and synaptic activity on the regulation of sodium and potassium voltage gated ion channels in embryonic Xenopus muscle cells after one day in culture

Hancock, Scott Stephen (1995) The effects of nerve-contact, membrane excitability, and synaptic activity on the regulation of sodium and potassium voltage gated ion channels in embryonic Xenopus muscle cells after one day in culture. Masters thesis, Memorial University of Newfoundland.

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Abstract

The kinetics, density and distribution of ion channels on myocytes are altered significantly during development, by genetic cues and extrinsic factors such as excitability, synaptic activity, and nerve-contact. The effects of such extrinsic factors on the developmental expression of ion channels in embryonic Xenopus myocytes is the focus of this work. Whole cell currents were recorded from embryonic Xenopus muscle cells after one day in culture using a List patch clamp and standard recording conditions. (Moody-Corbett and Gilbert, Dev. Br. Res., 1990, 55: 139-142). Na⁺ currents (INa) and three types of K⁺ currents inward rectifier (IR), inactivating (IIK), and non-inactivating (IK) outward rectifiers were recorded from both nerve-contacted and non-innervated muscle cells. The influence of membrane excitability and synaptic activity were examined by adding tetrodotoxin (TTX) and/or α-bungarotoxin (α-BTX) to the culture medium at the time of plating. Nerve-contact significantly increased the proportion of cells which displayed an INa and this increased expression was blocked when membrane excitability or synaptic activity was blocked. These results suggest that INa was maintained by a positive feedback mechanism while the upregulation of INa following nerve-contact was dependent on synaptic function. Nerve-contacted muscle cells had a significantly increased probability of expressing IIK than non-contacted muscle cells and this increase was not blocked when membrane excitability or synaptic activity was blocked. These results suggest that IIK was maintained by a separate mechanism than INa. It was concluded that nerve-contact, membrane excitability, and synaptic activity all play distinct and different roles in altering Na⁺ and K⁺ current expression.

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