Preferential support of Ca2+ uptake in smooth muscle plasma membrane vesicles by an endogenous glycolytic cascade

Studies of intact smooth muscle have suggested that its anomalous aerobic lactate production may reflect an intracellular compartmentation of glycolytic enzyme cascades designed to support specific exergonic processes. In particular, we have postulated a membrane-associated glycolytic cascade that preferentially supports the ATP requirements of membrane functions. We tested this hypothesis by using a smooth muscle plasma membrane fraction (PMV) purified for calcium pump activity. We show that glycolytic enzymes are endogenous in PMV and can produce NADH, ATP, and lactate from fructose 1,6-diphosphate in the presence of glycolytic cofactors. This glycolytic cascade can fuel the calcium pump despite the presence of an ATP trap that eliminated calcium uptake fueled by exogenously added ATP. This plasma membrane glycolytic cascade is coupled to calcium pump function in a tissue with both oxidative and glycolytic metabolism. Thus coupling of metabolic cascades with the specific processes they subserve may be a more general feature of cellular organization than was previously thought.