ATP Cycling Research Articles

Sarcoplasmic reticulum Ca-release channel and ATP-synthesis activities are early myocardial markers of heart failure produced by rapid ventricular pacing in dogs.

The contraction-relaxation cycle of the heart is dependent on a cycle of ATP production and utilization and a cycle of Ca uptake and Ca release by the sarcoplasmic reticulum (SR). Heart failure (HF) is associated with abnormalities of myocardial Ca and ATP cycling, but the time course of their development is unknown. This study tested the hypothesis that, compared with ATP-utilizing and Ca-uptake activities, decreases in ATP-synthesis and Ca-release activities occurred earlier in the development of HF and persisted longer during recovery from HF. HF was induced by right ventricular pacing of dogs at 250 beats/min. Dogs were studied after 1 week of pacing (n = 8, early HF), at HF (n = 11, severe HF), and 4 weeks after cessation of pacing (n = 9) and were compared with dogs not subjected to pacing. At early HF, there were decreased activities (p < 0.05) of the SR Ca-release channel (rate constant from 199 +/- 36 x 10(-4) to 90 +/- 16 x 10(-4) s-1), mitochondrial ATP synthesis (from 11.2 +/- 2.4 to 7.0 +/- 2.2 international units (IU)/g), and creatine kinase (CK) from 2028 +/- 266 to 1811 +/- 79 IU/g). The decreased Ca-channel activity was due to a 32% decrease in maximal activity (rate constant from 249 +/- 50 x 10(-4) to 170 +/- 29 x 10(-4) s-1) and to a 2-fold increase (from 19.1 +/- 12.4 to 42.0 +/- 14.2%) in inhibition of maximal channel activity (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of Adenosine-5’-Diphosphatase Activity in the Lactating Bovine Mammary Gland

A Ca2+- and Mg2+-stimulated adenosine-5’-diphosphatase has been found in lactating bovine mammary glands. The enzyme is associated with membranes of mitochondrial, microsomal, and Golgi apparatus fractions. The pH activity curves for the Golgi apparatus and microsomal fractions display two distinct maxima, one at pH 5.8 and the other between pH 7.4 and 8.4. Studies with activators and inhibitors indicate the enzyme is similar to adenosine-5’-diphosphatase found in other tissues. Its occurrence in the Golgi apparatus fraction indicates a possible role for this enzyme in the milk secretory process, particularly in ATP cycling in vesicles. Its occurrence in the microsomal fraction suggests a role in plasma membrane functioning.

Modulation of aortic protein phosphatase activity by polylysine.

The Ca2+-regulatory mechanism for contraction of smooth muscle involves phosphorylation of the 20,000-Da myosin light chains. In the fully relaxed muscle the intracellular concentration of Ca2+ is low ( 10-6M). Subsequently, formation of the Ca2+-calmodulin complex results in activation of myosin light-chain kinase and phosphorylation of the regulatory light chains. In this form, actin-myosin interaction is activated resulting in hydrolysis of ATP and cross-bridge cycling. The physiological correlate of these biochemical events is contraction of the smooth muscle cell (see (1–4) for reviews). Although recent studies suggest that cross bridges ma...

The effects of Frescon on molluscan hearts

1. Low concentrations of Frescon cause a slowing of heart rate in intact Bulinus. 2. In the isolated heart of Archachatina Frescon causes a contracture that ultimately cannot be opposed by the excitatory effects of 5-HT. 3. It is postulated that Frescon affects the calcium and ATP cycling mechanisms of the cardiac fibres.