Simulating the spread of membrane potential changes in arteriolar networks.

OBJECTIVE: Our aim was to simulate the spread of membrane potential changes in microvascular trees and then make the simulation programs accessible to other researchers. We have applied our simulations to demonstrate the implications of electrical coupling between arteriolar smooth muscle and endothelium.
METHODS: A two-layered, cable-like model of an arteriole was used, and the assumptions involved in the approach explicitly stated. Several common experimental situations that involve the passive spread of membrane potential changes in microvascular trees were simulated. The calculations were performed using NEURON, a well-established computer simulation program that we have modified for use with vascular trees.
RESULTS: Simulated results show that membrane potential changes would probably not spread as far in the endothelium as they would in the smooth muscle of arterioles. Where feed arteries are connected to larger distributing arteries, passive spread alone may not explain the physiologically observed spread of diameter changes.
CONCLUSIONS: Simulated results suggest that the morphology of an arteriole, in which the muscle layer is much thicker than the endothelium, favors electrical conduction along smooth muscle rather than the endothelium. However, it seems that passive electrical spread is insufficient to explain the apparent spread of membrane potential changes in experimental situations. Active responses involving voltage-dependent conductances may be involved, and these can also be included in our simulation.