Altered membrane potential control of contraction in arterial muscle in hypertension

Membrane potential has a different origin in the Kyoto-Wistar spontaneously hypertensive rat (SHR) arterial muscle cells compared to the normotensive Wistar-Kyoto rat (WKY) because of a higher activity of the electrogenic Na+ pump (Na+/K+-ATPase) in SHR. The activity of the Na+ pump is probably a good indicator of the state of Na+ loading of the vascular muscle cells, and is likely to be a partial compensation for increased SHR Na+ loading. The coupling mechanism might be altered due to excess intracellular free Na+ and diminished intracellular free K+, to a more electrogenic ratio of 3. The cause of higher intracellular Na+ and the resulting changes in Na+ transport is unknown, but there appears to be a trophic (long-term) influence of the sympathetic nervous system playing a key role, as shown by cross-innervation experiments.