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Biomedical subjects

H J Macherey

Publications and source records attributed to H J Macherey.

7 recordsLinked to original sources
PubMed1993

Electrogenic bicarbonate secretion in gallbladder: induction by barium via neuronal, possibly VIP-ergic pathways.

In guinea-pig gallbladder epithelium, cAMP converts electroneutral HCO3- secretion into an electrogenic process. The effects of blood side Ba2+ (5 mmol/l) on HCO3- transport were investigated in vitro, using pH-stat and voltage clamp techniques to determine unidirectional fluxes of HCO3- and transepithelial electrical characteristics. Serosal, not mucosal addition of Ba2+ elevated short-circuit current (Isc), transepithelial potential difference, and tissue conductance; it inhibited the absorptive HCO3- flux while leaving the secretory flux unchanged. The Isc effect of Ba2+ was inhibited or prevented by tetrodotoxin; D- and L-propranolol; the Cl- channel blocker 4-N-methyl-N-phenylaminothiophene-3-carboxylic acid; the intracellular Ca2+ antagonist, 3,4,5-trimethoxybenzoic acid 8-(diethylamino)ocytl ester; noradrenaline, by a yohimbine-sensitive action; somatostatin; HCO3(-)-free solutions. Thus Ba2+ appeared to release a neurotransmitter that gives rise to cAMP synthesis sufficient to turn part of electroneutral HCO3- secretion electrogenic. In a search for the involved signalling pathways, the H1-receptor antagonist, cetirizine, largely and hexamethonium, atropine, atenolol, indomethacin, and trifluoperazine entirely failed to antagonize the Isc effect of Ba2+. Similarly, carbachol, dobutamine, salbutamol, and serotonin were unable to mimic the action of Ba2+ and Isc effects of histamine were small and short-lived. By contrast, vasoactive intestinal peptide (VIP; 3 x 10(-7) mol/l) completely transformed HCO3- secretion into an electrogenic process. The VIP receptor antagonist (4Cl-DPhe6, Leu17) VIP, delayed and reduced the Isc responses to Ba2+ and VIP. As guinea-pig gallbladder epithelial cells possess cAMP-coupled VIP receptors close to VIPergic neurons, Ba2+ is likely to act by releasing VIP from neural terminals.

Alprostadil↗
PubMed1993

HCO3- reduces paracellular permeability of guinea pig duodenal mucosa by a Ca2+ (prostaglandin)-dependent action.

The mechanism of HCO3(-)-induced decrease in electrical conductance (Gt) of guinea pig duodenal mucosa was investigated in vitro. Gt and unidirectional fluxes of mannitol (M), Na+, and Cl- were straightly correlated. In the presence of HCO3- (20 mM), elevating the bath concentration of Ca2+ from 0 to 1.2 mM caused decreases in Gt and Na+ fluxes by approximately 30%. Smaller reductions were found in the absence of HCO-3. With the addition of Ca2+, Gt and unidirectional fluxes were lower with than without HCO3-. In the latter condition, PM/PNa, PM/PCl, and PNa/PCl (P is permeability) were close or equal to ratios predictable from free solution diffusion coefficients; with HCO3-, ratios became different or more different and PM/PNa was reduced. Straightly correlated were conductivities of six differently composed HCO3(-)-free salines and Gt of tissues bathed therein. This correlation did not embrace HCO3- Ringer. The Gt effect of Ca2+ (HCO3- present) was mimicked by prostaglandin E2 and reduced (by approximately 40%) by Ca2+ channel blockers (diltiazem, gallopamil), cyclooxygenase inhibitors (meclofenamate, diclofenac), cytochalasin D, and trifluoperazine. We conclude that without HCO3-, paracellular solute flow occurs mainly via structures resembling a free-solution shunt; HCO3-, through an action made more efficient by Ca(2+)-mediated prostaglandin synthesis and possibly involving microfilaments, strengthens a discriminatory barrier.

Animals↗
PubMed1993

Secretin and somatostatin as modulators of electrolyte transport in guinea pig gallbladder epithelium.

Effects of secretin and somatostatin on electrolyte transport by guinea pig gallbladder epithelium were investigated in vitro. Tissues were mounted in Ussing-type chambers and continuously short-circuited to measure tissue conductance, short-circuit current (Isc) and transepithelial voltage. Unidirectional fluxes (from mucosa to serosa: Jms; from serosa to mucosa: Jsm) of Na+ and Cl- were determined simultaneously by using tracer techniques and those of HCO3- by pH-stat titration. Serosal addition of secretin caused concentration-dependent increases in tissue conductance, Isc and (lumen-negative) transepithelial voltage. At 1.3 x 10(-8) M, secretin raised net HCO3- secretion by 1.5 mumol/cm2/hr, due to inhibition of Jms (from approximately 1.2 to approximately 0.7 mumol/cm2/hr) and stimulation of Jsm (from approximately 3.7 to approximately 4.7 mumol/cm2/hr). The associated increase in Isc by approximately 3.8 mumol/cm2/hr (up from approximately 0.5 mumol/cm2/hr) was not different from net HCO3-secretion (approximately 4 mumol/cm2/hr). Neither Na+ nor Cl- net fluxes accounted for secretin-induced Isc, both being absorbed at equal rates (Na+: approximately 2.7, down from approximately 4.6 mumol/cm2/hr; Cl-: approximately 2.5, down from approximately 6.4 mumol/cm2/hr). Secretin caused a 10-fold rise of luminal efflux of cyclic AMP that was mitigated by somatostatin, added at 6 x 10(-7) M to the serosal bath. Somatostatin inhibited secretin- and prostaglandin E1-induced Isc, but was ineffective in tissues stimulated with 8-Br-cyclic AMP. It partly reverted the effects of secretin on JmsHCO3 and JsmHCO3, but had no effects in untreated tissues. Our data indicate that secretin converts HCO3-secretion from an electroneutral into an electrogenic process and blocks part of NaCl absorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Electrogenic and electroneutral HCO3-secretion by guinea pig gallbladder epithelium: discriminatory abilities of Cl- channel blockers.

The specificity of Cl- channel blockers (including 5-nitro-2-(3-phenylpropylamino-)benzoic acid (NPPB), diphenylamine-carboxylic acid and 4-N-methyl-N-phenylaminothiophene-3-carboxylic acid (MPTC)) was studied in guinea pig gallbladder. This epithelium performs electroneutral HCO3- secretion, due to cell-to-lumen exit by Cl-/HCO3- exchange. At high intracellular cyclic AMP levels [produced by prostaglandin E1, (PGE1)], secretion turns electrogenic, secondary to induction of apical membrane Cl- and HCO3- conductances. Part of HCO3- secretion remains Cl(-)-dependent. Microelectrode, voltage-clamp and pH-stat techniques were used to determine membrane potentials, short-circuit current (Isc) and secretory HCO3- fluxes. With one exception, effective agents (concentration range 10(-5)-10(-4) M, luminal bath) including NPPB and diphenylamine-carboxylic acid inhibited secretory HCO3- fluxes in the presence and absence of PGE1 as well as PGE1-induced Isc. At 10(-4) M, inhibition of Isc was not attenuated by Cl- removal; however, NPPB effects were less at concentrations < 10(-4) M. MPTC (3 x 10(-5)-3 x 10(-4) M) only partly inhibited PGE1-induced Isc, was almost ineffective in Cl(-)-free solutions, and did not affect secretory HCO3- flux under any condition. Effects of NPPB and MPTC were distinct from those of the mitochondrial uncoupler, carbonyl cyanide p-trifluoromethoxy-phenylhydrazone. This agent (10(-7)-10(-5) M), failed to discriminate between Cl(-)-dependent and -independent Isc. In control tissues, 10(-5) M carboyl cyanide p-trifluoromethoxy-phenylhydrazone practically abolished membrane potentials, whereas 10(-4) M NPPB produced no change.(ABSTRACT TRUNCATED AT 250 WORDS)

Alprostadil↗
PubMed1991

Acid-induced increase in electrical conductance of guinea pig duodenal mucosa in vitro. Temporary protection by combined effects of bicarbonate and prostaglandin E2.

Electrical conductance as a sensitive indicator of acid damage has been investigated in guinea pig duodenal mucosa using Ussing-chamber techniques. Reductions of luminal pH from 7.4 to 3.0, 2.3, or 2.0 caused concentration-dependent, progressive increases in conductance, accompanied (pH 2.0) by a continuous increase in hydrogen permeation as determined by pH-stat titration. Increases in conductance and hydrogen flux were related to base-line conductance, with higher values conditioning for a sooner onset and/or more marked elevation. Conductance increases were prevented by timely back titration. Recently, it has been shown that serosal HCO3 reduces conductance by actions dependent on prostaglandins and serosal Na and sensitive to loop diuretics. Here, serosal HCO3 delayed the onset of acid-induced conductance increase by approximately 8 minutes, an effect reduced by omission of serosal Na and during exposure to serosal furosemide (10(-3) mol/L). In the presence of serosal indomethacin (10(-4) mol/L) and HCO3, prostaglandin E2 (10(-6) mol/L serosal bath) delayed the conductance increase. Because HCO3 secretion is negligible in this model, these results indicate effects of HCO3/prostaglandin E2 beyond mere buffering of invading hydrogen. These results are consistent with intracellular actions that tighten the paracellular pathway against acid and thus provide temporary protection from acid injury. In agreement with this view, HCO3 also limited conductance increases after luminal alkalinization by a furosemide-sensitive action.

Animals↗
PubMed1989

Rapid decrease in electrical conductance of mammalian duodenal mucosa in vitro. Combined effects of prostaglandin E2 and bicarbonate.

The effects of HCO3- on transepithelial conductance of guinea pig (and, in some experiments, rabbit) duodenum have been investigated using stripped preparations in Ussing-type chambers. Initial conductance amounted to approximately 27 mS/cm2. In the presence of serosal or bilateral HCO3- (20 mM), it fell to approximately 15 mS/cm2 within 60 min. With mucosal HCO3- or HCO3- -free solutions, conductance decreased to only approximately 23 mS/cm2. In the absence of HCO3-, serosal but not mucosal addition of HCO3- prompted a steep conductance drop that was 50% complete within 6 min. These effects were the same in proximal and distal segments, whereas conductance levels in the latter were higher. The effects of HCO3- required serosal Na+; they were partly prevented or reversed by serosal ouabain (3 x 10(-5) M), furosemide (10(-3) M), and other loop diuretics, and indomethacin (10(-5) M). Serosal addition of prostaglandin E2 (10(-7) M, followed by 10(-6) M) reduced conductance from approximately 22 to approximately 17 mS/cm2. This effect required serosal HCO3- and the presence of indomethacin. 8-Br-cyclic adenosine monophosphate (10(-3)M, serosal side) mimicked the effects of prostaglandin E2. Indomethacin and prostaglandin E2 did not influence the secretory flux of HCO3- (approximately 0.5 mumol/cm2.h, pH-stat method). Our results assign a critical role to serosal HCO3- in the maintenance of a low tissue permeability, dependent on the availability of prostaglandins (cyclic adenosine monophosphate) and involving HCO3- access to the cell rather than secretion.

8-Bromo Cyclic Adenosine Monophosphate↗