Showing papers by "Michael J. Berridge published in 1979"

Changes in calcium transport across calliphora salivary glands induced by 5-hydroxytryptamine and cyclic nucleotides

Abstract: The efflux of 45 Ca from prelabelled salivary glands was studied under a variety of conditions. 5-Hydroxytryptamine (5-HT) or cyclic AMP caused a large release of label most of which entered the saliva. The ionophore A23187 caused a similar release of calcium but EGTA had no effect. The presence of an active calcium pump on the lumenal surface was investigated further by studying calcium transport across the gland. This transport of calcium, which provides a measure of calcium entry into the cell, was very sensitive to 5-HT concentration but little affected by cyclic AMP. The small cyclic AMP-dependent transport was depressed by 8-bromo cyclic GMP with a parallel fall in the rate of fluid secretion. These studies provide more direct evidence that 5-HT acts to stimulate the entry of external calcium in addition to mobilizing internal calcium. Note: On sabbatical leave from the University of Massachusetts, Boston.

Cyclic nucleotide - calcium interactions in cell regulation

Abstract: Publisher Summary This chapter discusses the cyclic nucleotide–calcium interactions in cell regulation. Calcium enters cells either through agonist-dependent or voltage-dependent channels. The hydrolysis of phosphatidylinositol (PI) may play some role in calcium gating. The action of hormones or neurotransmitters is invariably associated with a specific hydrolysis of PI even though this phospholipid is usually a minor component of the membrane phospholipids. In the case of the insect salivary gland, there is a close relationship between the hydrolysis of PI and the entry of calcium during the actin 5-hydroxytryptamine under a variety of conditions. If the gland is stimulated with agents such as cyclic AMP or the ionophore A 23187, which bypass the 5-HT receptor, there is no hydrolysis of PI. It is found that in addition to stimulating the hydrolysis of PI, 5-HT also inhibits the synthesis of PI, which means that during prolonged stimulation, the level of this phospholipid will fall.