The effect of calcium channel blockade on basal- and substance P-induced intestinal secretion

Tachykinins in the gut. Part II. Roles in neural excitation, secretion and inflammation

The preprotachykinin-A gene-derived peptides substance (substance P; SP) and neurokinin (NK) A are expressed in intrinsic enteric neurons, which supply all layers of the gut, and extrinsic primary afferent nerve fibers, which innervate primarily the arterial vascular system. The actions of tachykinins on the digestive effector systems are mediated by three different types of tachykinin receptor, termed NK1, NK2 and NK3 receptors. Within the enteric nervous system, SP and NKA are likely to mediate, or comediate, slow synaptic transmission and to modulate neuronal excitability via stimulation of NK3 and NK1 receptors. In the intestinal mucosa, tachykinins cause net secretion of fluid and electrolytes, and it appears as if SP and NKA play a messenger role in intramural secretory reflex pathways. Secretory processes in the salivary glands and pancreas are likewise influenced by tachykinins. The gastrointestinal arterial system may be dilated or constricted by tachykinins, whereas constriction and an increase in the vascular permeability are the only effects seen in the venous system. Various gastrointestinal disorders are associated with distinct changes in the tachykinin system, and there is increasing evidence that tachykinins participate in the hypersecretory, vascular and immunological disturbances associated with infection and inflammatory bowel disease. In a therapeutic perspective, it would seem conceivable that tachykinin antagonists could be exploited as antidiarrheal, antiinflammatory and antinociceptive drugs.

The effect of calcium on gallbladder absorption

The absorption of water and electrolytes is an important physiologic function of the gallbladder which is altered during gallstone formation. Extracellular calcium and calcium channel antagonists are known to affect intestinal absorption, yet their effect on gallbladder absorption is less well defined. We, therefore, tested the hypothesis that changes in extracellular calcium or in calcium channels would alter gallbladder absorption. New Zealand white rabbit gallbladders were removed, filled with a modified Krebs buffer (Ca2+ = 0.7 mM), and suspended in an oxygenated bath of the same buffer. Water absorption was determined gravimetrically by obtaining serial gallbladder weights at 10-min intervals. After a 40-min control period, the serosal bathing solution was changed to one of four experimental solutions (n = 6 for each group): Ca2+ = 0.25, 0.7, or 1.2 mM or Ca2+ = 0.7 mM plus 0.1 mM verapamil. Absorption was determined during an 80-min experimental period with results expressed as the percentage change in gallbladder absorption compared to that of the control period. The 0.25, 0.7, and 1.2 mM Ca2+ groups did not show a significant change in absorption rate from their respective control rates. However, the verapamil group did demonstrate a significant (P less than 0.05) decrease in absorption rate of -69 +/- 8% by the end of the experimental period. These data demonstrate that verapamil inhibits gallbladder absorption while changes in serosal calcium concentration have no effect. We conclude that calcium channels and intracellular calcium may play an important role in modulating gallbladder absorption.