The Regulation of Respiration of Guinea Pig Taenia Coli in High-K Medium; The Role of Nicotinamide-Adenine Dinucleotide, Adenosine Diphosphate and Ca++

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Abstract
In an attempt to elucidate the regulation mechanism of respiration in the smooth muscle cell, the roles of NAD, ADP and Ca2+ were investigated in muscle respiration using the tissues and subcellular fractions from guinea pig taenia coli. The tension in the strips of taenia coli increased with a concomitant increase in O2 consumption in high-K medium (40 mM K) containing 2.5 mM Ca. 10-3 M Amytal and 10-5 M ouabain decreased the high-K induced tension and O2 consumption of the muscle. 10-4 M 2,4-dinitrophenol relieved the decreased respiration induced by ouabain, but not that with Amytal. NADH-linked respiration plays an important role in the respiration of the muscle. Ca2+ in concentrations ranging from 0.5 to 2.5 mM in the high-K medium resulted in an increase in tension and in O2 consumption progressively. In spectrophotometric observations of subcellular fractions of the taenia coli, ADP increased in absorbance change at 340 m.mu.. Such occurred in mitochondrial fractions and was initiated by the addition of NADH. The increase in ADP level of the cytoplasm possibly is due to a contraction triggered by Ca2+ thus stimulating respiration. At 0.1 mM of Ca2+ concentration, the muscle strip increased O2 consumption without tension development in high-K medium. In the spectrophotometric observations, Ca2+ and Sr2+ increased the absorbance change in the homogenate and in the mitochondrial fraction. One part of the Ca2+ entering into the smooth muscle treated with the high-K increased O2 consumption in mitochondria independent of an increase in muscle tension. NADH-linked respiration plays an important role in the smooth muscle respiration in high-K medium and that ADP and Ca2+ also play a role in regulating respiration.