Regional differences in electrical and mechanical properties of guinea-pig mesenteric vessels

Regional differences in electrical and mechanical properties of guinea-pig mesenteric vessels were investigated using microelectrode and isometric tension recording methods. The amplitude of membrane potentials differed according to region and in the following order; branch of jejunal artery (BJA) > cranial mesenteric artery (CMA) > jejunal artery (JA) greater than or equal to jejunal vein (JV) not equal to portal vein (PV). There were also regional differences in the muscle membrane potential with various concentrations of [K]o or [Na]o, while no differences were observed with applications of various concentrations of [Ca]o or [Cl]o. ACh produced hyperpolarization of the muscle membrane in the CMA, JA and JV but not in the PV and BJA. Hyperpolarization in the JA mainly followed increase in the K-permeability, and a reversal potential for ACh was distributed at about -70mV. In the JV, the ACh-induced hyperpolarization accompanied tension development. Phenylephrine depolarized the muscle membranes of the CMA, JA and PV but not of the BJA and JV. Low concentrations of phenylephrine produced contractions with no depolarization of the membrane in the JA and CMA. Isoprenaline-induced hyperpolarization was smaller in arteries than in veins, and this hyperpolarization was reduced in amplitude with repeated applications. The ACh-induced relaxation and phenylephrine-induced contraction were larger in the JA than in the CMA. Regional differences of the muscle property in response to application of different agents were discussed in relation to the physiological roles.