Calponin is not phosphorylated during contractions of porcine carotid arteries

Calponin and caldesmon were purified from porcine carotid arteries that were preincubated with [32P]orthophosphate, and the stoichiometry of phosphorylation was measured. In resting arteries, caldesmon was phosphorylated to a level of 0.41 mol PO4/mol protein, while calponin was phosphorylated to levels < 0.01 mol PO4/mol protein. Stimulation by histamine (1 or 5 min), KCl (1, 5 or 60 min), or phorbol 12,13-dibutyrate (PDBu; 1 microM for 15 or 60 min) did not lead to measurable increases in the PO4 content of calponin. Because dephosphorylation of calponin during the purification procedure could account for these results, we also determined stoichiometries after firat denaturing endogenous phosphatases with trichloroacetic acid. In these experiments, calponin was determined to be phosphorylated to the same low levels as in the first set of experiments. Collectively, these data show that calponin is not phosphorylated to significant levels during contractions of carotid arteries under conditions where caldesmon phosphorylation is apparent. The circumstances under which calponin may be phosphorylated in intact smooth muscle, and the purpose that may be served by this potential regulatory process, remain to be determined.

Chloride transport of frog gastric fundus: effects of omeprazole

Omeprazole (10(-4) M) inhibited H+ secretion and increased potential difference (PD), resistance, and short-circuit current (Isc) in chambered bullfrog gastric mucosa, but the electrical changes developed only in tissues previously exposed to histamine. Net chloride transport (JnetCl) did not change after omeprazole under short-circuited conditions, and Isc increased to become equal to JnetCl. Under open-circuit conditions, JnetCl was reduced by 38%, the decrement attributable to the concomitant increase in PD, as evidenced by a linear relationship between JnetCl and PD in omeprazole-treated mucosae clamped to different PD (0-45 mV). The effect of omeprazole on PD and Isc could be blocked by metiamide and was absent in spontaneously resting tissues. HEPES nutrient solutions did not alter the electrical response or Cl- transport after omeprazole. In Na+-free solutions, omeprazole induced only a transient rise in PD and Isc. We conclude that omeprazole uncouples H+ and Cl- secretion. This Cl- secretion is electrogenic and dependent upon stimulation by histamine. Both Na+ and HCO3- seem to be involved in movement of Cl- across the basolateral membrane.

Prolactin and growth hormone secretion in chickens: stimulation by histamine and inhibition by gamma-aminobutyric acid

Anterior pituitary glands from chickens (Gallus domesticus) were incubated with or without single, mediobasal chicken hypothalami in medium containing histamine, alone or together with the antagonist diphenhydramine or in medium containing gamma-aminobutyric acid (GABA), alone or together with the antagonists bicuculline or picrotoxin. The release of prolactin (Prl) and growth hormone (GH) was measured by homologous radioimmunoassay. Histamine had no direct effect on the release of either hormone but stimulated Prl (in a dose-related way) and GH release when anterior pituitary glands were co-incubated with hypothalami. Diphenhydramine also had no direct effect on Prl or GH secretion but blocked the stimulatory effect of histamine on hypothalamusinduced Prl and GH release. When anterior pituitary glands were incubated without hypothalami, GABA, bicuculline and picrotoxin had no effect on the release of Prl or GH. However, GABA inhibited the release of both hormones in a concentration-related manner, when anterior pituitary glands were co-incubated with hypothalami. This inhibition was blocked by both bicuculline and picrotoxin. These results suggest that histamine and GABA may be involved in controlling the secretion of Prl and GH from the avian pituitary gland, possibly by modifying the secretion of hypothalamic releasing and/or release-inhibiting hormones.

Invariant relation between total acid secretion and secretagogue exposure: secretory dynamics in bullfrog

Using a continuous recording of acid secretion in frog gastric mucosa by pH-stat interfaced with a microcomputer, the pattern of secretion rate was studied under variable concentrations and durations of stimulation by histamine and forskolin. This tissue can respond with only a limited range of secretory rates. Larger concentrations and/or longer durations of stimulation may result in a secretion rate pattern prolonged far beyond the duration of stimulation. Although for the concentration-response curve the steady-state or peak acid secretion varies with the duration of stimulation, total acid secreted as a function of exposure to stimulator (time integral of the stimulatory pattern) is independent of the stimulatory pattern.

Histamine-Evoked Nasal Secretion in the Dog

Nasal secretory activity was measured in seven dogs in response to topical stimulation by histamine and methacholine. The methacholine response was blocked by atropine but not by chlorpheniramine. The histamine response was blocked by chlorpheniramine but not by atropine. These results suggest that there are two independent mechanisms of nasal secretion in the dog.