Localization of basic drugs in the submaxillary gland

Modulation of ACh-induced currents in rat adrenal chromaffin cells by ligands of alpha2 adrenergic and imidazoline receptors

The aim of this study was to investigate the expression of the alpha2-adrenergic receptors in the adrenal medulla, and to examine the mechanism by which clonidine and related drugs inhibit acetylcholine (ACh)-induced whole-cell currents in adrenal chromaffin cells. Reverse transcription-polymerase chain reaction (RT-PCR) performed on punches of rat adrenal medulla demonstrated expression of mRNA for the 2A-, alpha2B- and alpha2C-adrenergic receptors. Similar experiments conducted with tissue punches obtained from the adrenal cortex did not reveal expression of these receptor subtypes. Whole-cell currents were recorded in isolated chromaffin cells using the perforated-patch configuration. ACh (50 microM) evoked inward currents with a peak amplitude of 117.8+/-9.3 pA (n = 45; Vhol = -60 mV). The currents were inhibited in a dose-dependent manner (0.5-50 microM) by clonidine, UK 14,304 and rilmenidine (agonists of alpha2/imidazoline receptors), as well as by SKF 86466 and efaroxan (antagonists). Adrenaline and noradrenaline (50-100 microM) had no significant effect. Thus, although the adrenal medulla expresses mRNA for the alpha2-adrenergic receptors, the lack of agonist-antagonist specificity observed in our whole-cell recordings (in the absence of intracellular dialysis) provides additional evidence against the possibility that these inhibitory effects are mediated by classical alpha2 or imidazoline receptor interactions.

Continuous fluorometric measurement of intracellular pH and Ca2+ in perfused salivary gland and pancreas

Intracellular pH (pHi) has been measured in intact, perfused rat mandibular salivary glands loaded with the fluorescent pH indicator BCECF [2',7'-bis(2-carboxyethyl)-5(6)- carboxyfluorescein]. Glands mounted in the cuvette of a conventional bench-top spectro-fluorometer were perfused for 5 min with the acetoxymethyl ester of BCECF and fluorescence was measured ratiometrically at 6-s intervals. The mean value of pHi in glands perfused with a HCO3(-)-free, N-2-hydroxyethylpiperazine-N'-2- ethanesulphonic acid (HEPES)-buffered solution at 37 degrees C was 7.36 +/- 0.01 (n = 52) which is comparable with values obtained by 31P nuclear magnetic resonance (NMR) spectroscopy. NMR data confirmed that the BCECF loading period was accompanied by a transient acidification of the cells, but there was no significant change in the content of the major phosphorus metabolites. Changes in pHi in response to NH4Cl pulses and acetylcholine stimulation were comparable with results reported previously for isolated acini. Additional, preliminary experiments show that the method can also be used to monitor intracellular Ca2+ (using fura-2) in perfused salivary glands, and can be adapted for studies of the isolated, perfused pancreas.

Acetylcholine receptor channels and their block by clonidine in cultured bovine chromaffin cells

1. Acetylcholine (10-50 microM) applied to bovine chromaffin cells under whole-cell voltage clamp produced an inward current and an increase in the noise level of the current trace. At concentrations greater than or equal to 20 microM the ACh current desensitized with time. Spectral analysis of the ACh-induced increase in current noise showed that it could be fitted by a single Lorentzian component with a time constant, tau noise = 11 +/- 0.9 ms (Vm = -80 mV). 2. Clonidine (2-30 microM) markedly reduced the size of the ACh-induced whole-cell current, and altered the shape of the noise spectrum. In the presence of clonidine, ACh noise spectra were fitted by two Lorentzian components with time constants which varied with clonidine concentration. The single-channel conductance from noise (gamma = 24 pS) was unaltered by clonidine. 3. The reduction in the size of the whole-cell ACh current, produced by clonidine, was not mimicked by adrenaline (at concentrations up to 60 microM). GABA-induced whole-cell currents and spectra of GABA noise were also unchanged suggesting that the effect of clonidine was specific for the ACh receptor channel. 4. When applied intracellularly (from the patch pipette) clonidine had no apparent influence on the whole-cell ACh current. Furthermore, when clonidine was perfused over the cell surface at a concentration sufficient to block the whole-cell ACh response, single ACh channels could still be recorded under the patch-pipette tip (i.e. in cell-attached patches, not exposed to clonidine). 5. Clonidine block showed little voltage dependence; the peak ACh current remained linearly dependent on clamp potential. In addition, the fast and slow time constants derived from ACh noise spectra in the presence of clonidine did not show the sort of dependence on antagonist concentration expected for simple channel block; this suggests that clonidine has a complex blocking action. 6. Single ACh channels recorded in outside-out patches had a conductance of gamma = 39 +/- 0.7 pS, although a subpopulation of smaller and larger events also occurred in some patches. The mean single-channel conductance in outside-out patches was unaltered by clonidine. 7. Under normal conditions the kinetics of single ACh channels were more complex than suggested from noise analysis. Burst length distributions could be described by two exponential components with fast and slow time constants of tau f = 0.69 +/- 0.17 and tau s = 9.51 +/- 0.84 ms.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of perfused rat mandibular-gland pHI on the ratio of procainamide concentration in saliva to that in venous effluent

The saliva to venous-effluent concentration ratio (S/E ratio) for procainamide (PA) was determined and compared with the ratio calculated by using the intracellular pH value of glandular cells. Exposed mandibular gland was perfused in situ with Krebs-Ringer bicarbonate buffer containing PA (10-100 micrograms/ml) and acetylcholine (ACh, 0.1 to 10 microM) or pilocarpine (10 microM). These perfusion conditions maintained almost normal physiological function of the mandibular gland throughout the perfusion period of 60 min, since the salivary Na+ and K+ concentrations were kept at almost constant levels, comparable with those reported in vivo, and the salivary flow, pH and protein level were also stabilized. Under fixed stimulation conditions with 1 microM ACh or 10 microM pilocarpine, the perfusate PA concentration ranging from 20 to 100 micrograms/ml did not affect the S/E ratio (approximately 0.3). There was a negative correlation between the S/E ratio and salivary pH when stimulated with 0.1 to 10 microM ACh. However, Matin's equation [S. B. Matin et al., Clin. Pharmac. Ther. 16, 1052 (1974)] employing venous effluent and salivary pH values did not explain fully these observed ratios. In contrast, Borzelleca's model [J. F. Borzelleca and J. W. Putney, J. Pharmac. exp. Ther. 174, 527 (1970)] for salivary drug transport using intracellular pH of the mandibular gland cells predicted S/E ratios relatively close to the observed values when the gland was perfused at pH 7.4 or 8.0.

Differential effects of aldosterone and ADH on intracellular electrolytes in the toad urinary bladder epithelium

Quantitative electron microprobe analysis was employed to compare the effects of aldosterone and ADH on the intracellular electrolyte concentrations in the toad urinary bladder epithelium. The measurements were performed on thin freeze-dried cryosections utilizing energy dispersive x-ray microanalysis. After aldosterone, a statistically significant increase in the intracellular Na concentration was detectable in 8 out of 9 experiments. The mean Na concentration of granular cells increased from 8.9 +/- 1.3 to 13.2 +/- 2.2 mmol/kg wet wt. A significantly larger Na increase was observed after an equivalent stimulation of transepithelial Na transport by ADH. On average, the Na concentration in granular cells increased from 12.0 +/- 2.3 to 31.4 +/- 9.3 mmol/kg wet wt (5 experiments). We conclude from these results that aldosterone, in addition to its stimulatory effect on the apical Na influx, also exerts a stimulatory effect on the Na pump. Based on a significant reduction in the Cl concentration of granular cells, we discuss the possibility that the stimulation of the pump is mediated by an aldosterone-induced alkalinization. Similar though less pronounced concentration changes were observed in basal cells, suggesting that this cell type also participates in transepithelial Na transport. Measurements in mitochondria-rich cells provided no consistent results.

Intracellular pH in the rat mandibular salivary gland: the role of Na-H and Cl-HCO3 antiports in secretion

Intracellular pH (pHi) in the perfused rat mandibular gland was determined from the distribution of DMO (5,5-dimethyl-2,4-oxazolidinedione). In unstimulated glands, pHi averaged 7.12 +/- 0.02. Stimulation with a "standard" (submaximal) concentration (0.3 mumol/l) of acetylcholine (ACh) caused a fall in pHi to 6.81 +/- 0.06 over 60 min, but a maximal concentration (1.0 mumol/l) caused an initial rise in pHi to 7.60 +/- 0.02, followed by a fall to 7.45 +/- 0.02 over 60 min. After replacement of perfusate Cl with gluconate, the standard ACh concentration caused a rise in pHi to 7.50 +/- 0.02 followed by a fall to 7.27 +/- 0.04 after 60 min, concomitant with a 76% fall in secretory rate and a rise in salivary HCO3 concentration from 14 +/- 0.9 to 67 +/- 1.5 mmol/l. Furosemide (1 mmol/l) had a similar effect to gluconate replacement except that secretory rate fell only by 60%. Bumetanide (1 mmol/l), which inhibited secretion by 67%, did not cause pHi to rise following ACh stimulation but prevented the fall seen with ACh alone. Acetazolamide and methazolamide (1 mmol/l) had no effect on the salivary secretory response to ACh but they caused pHi to rise, respectively, to 7.20 +/- 0.03 and 7.43 +/- 0.02. Bumetanide and methazolamide together caused pHi to rise to 7.58 +/- 0.02 and reduced the secretory response to ACh by 91%. The disulfonic stilbene, SITS, caused pHi to rise to 7.26 +/- 0.03. Ouabain and amiloride both caused resting pHi to fall closer to equilibrium and largely abolished the gland's responsiveness to ACh.(ABSTRACT TRUNCATED AT 250 WORDS)