Metabolic differences between norepinephrine- and K+-stimulated anococcygeus muscle

The effects of norepinephrine (NE) and K+ stimulation on aerobic glycolysis (JLac), O2 utilization (JO2), and isometric force of isolated rat anococcygeus smooth muscle were investigated to determine the relationship between metabolism and contractility. A large sustained increase in JLac was measured during NE stimulation, but only a small rise in JLac occurred during high-KCl depolarization. JO2, in both cases, correlated with the force response. The difference in JLac could not be explained solely on the lower force output of K+-depolarized muscles or on increased glycogenolysis during NE stimulation, but was perhaps due to activation of energy-requiring processes associated with receptor- rather than depolarization-mediated Ca2+ mobilization. When muscles were stimulated with a K2SO4 (substituted for NaCl) Krebs-Ringer bicarbonate (KRB) rather than a N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered medium, JLac was significantly elevated due to an increased intracellular pH as a result of the low external Cl-. Lowering the pH of KRB or adding the anion exchange inhibitor 4-4'-diisothiocyanostilbene-2,2'disulfonic acid prevented the rise in JLac and also restored the initial fast component of the force response to NE in Cl(-)-free solution.