Effects of phenylephrine on membrane currents in single smooth muscle cells of taenia caeci

Procedures used for dissociation of taenia caeci smooth muscle cells usually damage alpha 1-adrenoceptors. This paper describes modes of isolation under which alpha 1-adrenoceptors of taenia caeci do not lose their function. It has been found that antioxidants (dithiothreitol or taurine) are able to protect receptors from injury caused by digestive enzymes. A high concentration of bovine serum albumin also protects receptors from enzyme injury if a relatively specific enzyme (collagenase Type XI, Sigma) is used. Phenylephrine (10 mcmol/l) studied both in muscle strips using the double sucrose gap method and in isolated smooth muscle cells using whole cell current clamp conditions substantially hyperpolarized the smooth muscle membrane. This hyperpolarization was blocked by pretreatment of the tissues or cells by prazosin (1 mcmol/l). Phenylephrine (1-50 mcmol/l), under whole cell patch clamp conditions, enhanced the frequency and amplitude of spontaneous transient outward currents (STOCs), which were voltage- and temperature-dependent, and elicited a low amplitude sustained outward current. Phenylephrine (10 mcmol/l) reduced the inward and enhanced the outward component of the total whole cell current evoked by voltage steps from the holding potential of -50 mV to -10 mV. Under experimental conditions when only calcium current was recorded, phenylephrine significantly enhanced its amplitude. These results are in favor of the assumption that phenylephrine induced hyperpolarization is at least partially the consequence of calcium influx, which activates potassium conductance.