Energy Production in Rat Parotid Gland

Abstract

Rat parotid gland slices showed a very slow rate of glucose utilization and lactic acid produca tion, both in the presence and in the absence of oxygen. Epinephrine. which caused rapid enzyme secretion by the slices did not affect the low rate of glycolysis.A rough calculation indicates that in the parotid gland ATP is produced by oxidative phosphorylation 50 times faster than by glycolysis. The mitochondria, when isolated and tested in presence of EDTA or EGTA showed respiratory activity and respiratory control comparable to those of liver mitochondria. Adenosine 3' : 6'-cyclic phosphate, which is an intermediate in induction of enzyme secretion, showed no clear-cut effect on the functions of the parotid mitochondria. Isolation of the mitochondria in the absence of the above chelators yielded a preparation which was almost depleted of NAD, respired feebly on NAD linked substrates and showrd no respiratory control. Addition of NADf restored respiration. The damage caused to these mitochondria during isolation was attributed to the high calcium concentrations found in the gland. Addition of small amounts of free calcium to functional parotid mitochondria indeed caused the loss of NAD and the decline of respiration. Tested in parallel experiments, liver mitochondria were much more resistant t o added calcium. Their initial calcium content was one tenth that of the parotid mitochondria. The control of calcium distribution in the parotid gland and the possible functions of calcium are discussed.Previous work showed that adenosine 3' : 5' cyclic phosphate (Ado-3' : 5'-P) is a n intermediate in the induction of enzyme secretion in rat parotid gland [l]. It had also been found that the secretion process in exocrine glands is critically dependent on energy [2-41. It therefore seemed possible that Ado-3': 5'-P controls the secretion process by acting on a step of energy supply. Since there is little information on the energy producing systems of exocrine glands it was decided t o investigate these systems in some detail. It will be shown in the present work that the glycolytic activity of the parotid gland is very poor and therefore probably unable to produce enough ATP for secretion. On the other hand, the mitochondria contained efficient ATP producing systems which were unaffected by Ado-3':5'-P. Calcium which was found in very high concentration in the gland seemed t o cause, in the absence of EDTA, extensive damage to the mitochondria, including depletion of NAD. MATERIALS ASD METHODS Rat Parotid Slices SystemExperiments were carried out according t o the procedure previously used [3]. At the beginning and termination of the experiments relevant analyses were performed on slices and on incubation medium. Isolation of a Mitochondria1 Fraction from Parotid GlandAll manipulations were carried out a t 0"-4". Glands were collected in 0.25 M sucrose adjusted to pH 7.5 with sodium bicarbonate. A homogenate was prepared in sucrose medium (0.25 M sucrose, 0.5 mM EDTA and 0.5 mM EGTA, pH 7.5). Sucrose medium with I mM EDTA wi...

Calcium and pancreatic secretion. I. Subcellular distribution of calcium and magnesium in the exocrine pancreas of the guinea pig.

“…Thus, concentrations comparable to those we observed in the pancreas of the guinea pig have been previously found in the salivary glands (parotid, sublingual, and submandibular) (5,33,34), as well as in the adrenal medulla (35), whereas much lower levels have been found in tissues which are not so highly specialized towards secretion, such as the liver (36).…”

Effects of adrenergic agonists on the oxygen uptake and amylase output in rat submandibular gland slices.

“…The increase in K+ release due to adrenaline is not mediated by changes in the concentration of cyclic AMP in the cells . On the other hand, the secretory process of amylase is mediated by cyclic AMP (4,5,12,15). In the present experiment, the adrenaline stimulation of the amylase output was abolished by the addition of propranolol.…”

Calcium and Gastrointestinal Secretion

“…The description of a microsomal fraction in rat parotid [94] and submaxillary [1.94] glands which demonstrates ATP-dependent calcium uptake supports this possibility [though a similar system apparently exists in the adrenal medulla: 79], but mitochondria or other intracellular organelles might also serve as the source of calcium. It also accounts for the large store of calcium within the salivary glands [37] which, if present in other exocrine glands, may perhaps explain why the effect of calcium-lack are slow to develop.…”