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Biomedical subjects

D G Welsh

Publications and source records attributed to D G Welsh.

18 recordsLinked to original sources
PubMed2004

TRPC3 mediates pyrimidine receptor-induced depolarization of cerebral arteries.

We tested the hypothesis that TRPC3, a member of the canonical transient receptor potential (TRP) family of channels, mediates agonist-induced depolarization of arterial smooth muscle cells (SMCs). In support of this hypothesis, we observed that suppression of arterial SMC TRPC3 expression with antisense oligodeoxynucleotides significantly decreased the depolarization and constriction of intact cerebral arteries in response to UTP. In contrast, depolarization and contraction of SMCs induced by increased intravascular pressure, i.e., myogenic responses, were not altered by TRPC3 suppression. Interestingly, UTP-evoked responses were not affected by suppression of a related TRP channel, TRPC6, which was previously found to be involved in myogenic depolarization and vasoconstriction. In patch-clamp experiments, UTP activated a whole cell current that was greatly reduced or absent in TRPC3 antisense-treated SMCs. These results indicate that TRPC3 mediates UTP-induced depolarization of arterial SMCs and that TRPC3 and TRPC6 may be differentially regulated by receptor activation and mechanical stimulation, respectively.

Animals↗
PubMed2001

Mechanisms of coronary artery depolarization by uridine triphosphate.

We sought to define the basic mechanisms by which pyrimidine nucleotides constrict rat coronary resistance arteries. Uridine triphosphate (UTP) caused a dose-dependent constriction in coronary arteries stripped of endothelium. UTP also depolarized and increased cytosolic Ca2+ in coronary smooth muscle cells. Nisoldipine, an antagonist of voltage-operated Ca2+ channels, blocked the rise in cytosolic Ca2+ and reduced UTP-induced vasoconstriction by approximately 75% which suggests a prominent role for depolarization in this constrictor response. The ionic basis of UTP-induced depolarization was subsequently explored in coronary smooth muscle cells using whole-cell patch-clamp electrophysiology. In the absence of K+ and with CsCl in the pipette, UTP (40 microM) activated a sustained inwardly rectifying current (-0.66 +/- 0.10 pA/pF at -60 mV). A 100 mM reduction in bath Na+ shifted the reversal potential of this current (from -2 +/- 1 to -28 +/- 4 mV) and reduced the magnitude (from -2.26 +/- 0.61 to -0.51 +/- 0.11 pA/pF). In addition to activating a depolarizing cation current, UTP inhibited hyperpolarizing outward currents. Specifically, UTP inhibited ATP-sensitive and voltage-dependent K+ currents yet had no effect on inwardly rectifying and Ca2+-activated K+ channels. This study indicates that electromechanical coupling is integral to pyrimidine-induced constriction in coronary resistance arteries.

Animals↗
PubMed2000

Swelling-activated cation channels mediate depolarization of rat cerebrovascular smooth muscle by hyposmolarity and intravascular pressure.

1. Increases in intravascular pressure depolarize vascular smooth muscle cells. Based on the attenuating effects of Cl- channel antagonists, it has been suggested that swelling-activated Cl- channels may be integral to this response. Consequently, this study tested for the presence of a swelling-activated Cl- conductance in both intact rat cerebral arteries and isolated rat smooth muscle cells. 2. A 50 mosmol l-1 hyposmotic challenge (300 to 250 mosmol l-1) constricted rat cerebral arteries. This constriction contained all the salient features of a pressure-induced response including smooth muscle cell depolarization and a rise in intracellular Ca2+ that was blocked by voltage-operated Ca2+ channel antagonists. The hyposmotically induced depolarization was attenuated by DIDS (300 microM) and tamoxifen (1 microM), a response consistent with the presence of a swelling-activated Cl- conductance. 3. A swelling-activated current was identified in cerebral vascular smooth muscle cells. This current was sensitive to Cl- channel antagonists including DIDS (300 microM), tamoxifen (1 microM) and IAA-94 (100 microM). However, contrary to expectations, the reversal potential of this swelling-activated current shifted with the Na+ equilibrium potential and not the Cl- equilibrium potential, indicating that the swelling-activated current was carried by cations and not anions. The swelling-activated cation current was blocked by Gd3+, a cation channel antagonist. 4. Gd3+ also blocked both swelling- and pressure-induced depolarization of smooth muscle cells in intact cerebral arteries. 5. These findings suggest that swelling- and pressure-induced depolarization arise from the activation of a cation conductance. This current is inhibited by DIDS, tamoxifen, IAA-94 and gadolinium.

Animals↗
PubMed2000

Role of EDHF in conduction of vasodilation along hamster cheek pouch arterioles in vivo.

We tested whether local and conducted responses to ACh depend on factors released from endothelial cells (EC) in cheek pouch arterioles of anesthetized hamsters. ACh was delivered from a micropipette (1 s, 500 nA), while arteriolar diameter (rest, approximately 40 microm) was monitored at the site of application (local) and at 520 and 1,040 microm upstream (conducted). Under control conditions, ACh elicited local (22-65 microm) and conducted (14-44 microm) vasodilation. Indomethacin (10 microM) had no effect, whereas N(omega)-nitro-L-arginine (100 microM) reduced local and conducted vasodilation by 5-8% (P < 0.05). Miconazole (10 microM) or 17-octadecynoic acid (17-ODYA; 10 microM) diminished local vasodilation by 15-20% and conducted responses by 50-70% (P < 0.05), suggesting a role for cytochrome P-450 (CYP) metabolites in arteriolar responses to ACh. Membrane potential (E(m)) was recorded in smooth muscle cells (SMC) and in EC identified with dye labeling. At rest (control E(m), typically -30 mV), ACh evoked local (15-32 mV) and conducted (6-31 mV) hyperpolarizations in SMC and EC. Miconazole inhibited SMC and EC hyperpolarization, whereas 17-ODYA inhibited hyperpolarization of SMC but not of EC. Findings indicate that ACh-induced release of CYP metabolites from arteriolar EC evoke SMC hyperpolarization that contributes substantively to conducted vasodilation.

Animals↗
PubMed2000

NaHCO(3) and KHCO(3) ingestion rapidly increases renal electrolyte excretion in humans.

This paper describes and quantifies acute responses of the kidneys in correcting plasma volume, acid-base, and ion disturbances resulting from NaHCO(3) and KHCO(3) ingestion. Renal excretion of ions and water was studied in five men after ingestion of 3.57 mmol/kg body mass of sodium bicarbonate (NaHCO(3)) and, in a separate trial, potassium bicarbonate (KHCO(3)). Subjects had a Foley catheter inserted into the bladder and indwelling catheters placed into an antecubital vein and a brachial artery. Blood and urine were sampled in the 30-min period before, the 60-min period during, and the 210-min period after ingestion of the solutions. NaHCO(3) ingestion resulted in a rapid, transient diuresis and natriuresis. Cumulative urine output was 44 +/- 11% of ingested volume, resulting in a 555 +/- 119 ml increase in total body water at the end of the experiment. The cumulative increase (above basal levels) in renal Na(+) excretion accounted for 24 +/- 2% of ingested Na(+). In the KHCO(3) trial, arterial plasma K(+) concentration rapidly increased from 4.25 +/- 0.10 to a peak of 7.17 +/- 0.13 meq/l 140 min after the beginning of ingestion. This increase resulted in a pronounced, transient diuresis, with cumulative urine output at 270 min similar to the volume ingested, natriuresis, and a pronounced kaliuresis that was maintained until the end of the experiment. Cumulative (above basal) renal K(+) excretion at 270 min accounted for 26 +/- 5% of ingested K(+). The kidneys were important in mediating rapid corrections of substantial portions of the fluid and electrolyte disturbances resulting from ingestion of KHCO(3) and NaHCO(3) solutions.

Acid-Base Equilibrium↗
PubMed1999

Spread of vasodilatation and vasoconstriction along feed arteries and arterioles of hamster skeletal muscle.

1. In arterioles of the hamster cheek pouch, vasodilatation and vasoconstriction can spread via the conduction of electrical signals through gap junctions between cells that comprise the vessel wall. However, conduction in resistance networks supplying other tissues has received relatively little attention. In anaesthetized hamsters, we have investigated the spread of dilatation and constriction along feed arteries and arterioles of the retractor muscle, which is contiguous with the cheek pouch. 2. When released from a micropipette, acetylcholine (ACh) triggered vasodilatation that spread rapidly along feed arteries external to the muscle and arterioles within the muscle. Responses were independent of changes in wall shear rate, perivascular nerve activity, or release of nitric oxide, indicating cell-to-cell conduction. 3. Vasodilatation conducted without decrement along unbranched feed arteries, yet decayed markedly in arteriolar networks. Thus, branching of the conduction pathway dissipated the vasodilatation. 4. Noradrenaline (NA) or a depolarizing KCl stimulus evoked constriction of arterioles and feed arteries of the retractor muscle that was constrained to the vicinity of the micropipette. This behaviour contrasts sharply with the conduction of vasodilatation in these microvessels and with the conduction of vasoconstriction elicited by NA and KCl in cheek pouch arterioles. 5. Focal electrical stimulation produced constriction that spread rapidly along feed arteries and arterioles. These responses were inhibited by tetrodotoxin or prazosin, confirming the release of NA along perivascular sympathetic nerves, which are absent from arterioles studied in the cheek pouch. Thus, sympathetic nerve activity co-ordinated the contraction of smooth muscle cells as effectively as the conduction of vasodilatation co-ordinated their relaxation. 6. In the light of previous findings in the cheek pouch, the properties of vasoconstriction and vasodilatation in feed arteries and arterioles of the retractor muscle indicate that substantive differences can exist in the nature of signal transmission along microvessels of tissues that differ in structure and function.

Animals↗
PubMed1999

Efflux of T4 from the in situ perfused liver of rainbow trout: effect of T4, dithiothreitol and cysteine in the perfusate.

A Cortland saline-perfused rainbow trout (Oncorhynchus mykiss) liver model was used to study aspects of T4 efflux from the intact organ system. There was a consistent efflux of T4 in the absence of T4 in the perfusate, and the T4 efflux was increased in the presence of T4 in the perfusate, but the efflux was not T4-dose dependent. The addition of the thiol-containing compound dithiothreitol (DTT, 2 mM) to the perfusate had no significant effect on the flux of T4 from the liver, whereas the addition of cysteine (2 mM), a thiol-containing amino acid suppressed T4 efflux. The results are consistent with the known mechanisms of thyroid hormone trafficking across cell membranes, and suggest that organ systems, such as the liver, may act as a major reserve of hormone, thus participating in plasma thyroid hormone homeostasis.

Animals↗
PubMed1999

Role of skeletal muscle in plasma ion and acid-base regulation after NaHCO3 and KHCO3 loading in humans.

This paper examines the time course of changes in plasma electrolyte and acid-base composition in response to NaHCO3 and KHCO3 ingestion. It was hypothesized that skeletal muscle is involved in the correction of the ensuing plasma disturbance by exchanging ions, gasses, and fluids between cells and extracellular fluids. Five male subjects, with catheters in a brachial artery and antecubital vein, ingested 3.57 mmol/kg body mass NaHCO3 or KHCO3. While seated, blood samples were taken 30 min before ingestion of the solution, at 10-min intervals during the 60-min ingestion period, and periodically for 210 min after ingestion was complete. Blood was analyzed for gases, hematocrit, plasma ions, and total protein. With NaHCO3, arterial plasma Na+ concentration ([Na+]) increased from 143 +/- 1 to 147 +/- 1 (SE) meq/l, H+ concentration ([H+]) decreased by 6 +/- 1 neq/l, and PCO2 increased by 5 +/- 1 mmHg. There was no detectable net Na+ uptake by tissues. An increased plasma strong ion difference ([SID]) accounted fully for the decrease in plasma [H+]. With KHCO3, K+ concentration increased from 4.25 +/- 0.10 to 7.17 +/- 0.13 meq/l, plasma volume decreased by 15.5 +/- 2.3%, [H+] decreased by 4 +/- 1 neq/l, and there was no change in PCO2. The decrease in [H+] in the KHCO3 trial primarily arose in response to the increased [SID]. Net K+ uptake by tissues accounted for 37 +/- 5% of the ingested K+. In conclusion, ingestion of NaHCO3 and KHCO3 produced markedly different fluid and ionic disturbances and associated regulatory responses by skeletal muscle. Accordingly, the physicochemical origins of the acid-base disturbances also differed between treatments. The tissues did not play a role in regulating plasma [Na+] after ingestion of NaHCO3. In contrast, the net influx of K+ to tissues played an important role in removing K+ from the extracellular compartment after ingestion of KHCO3.

Acid-Base Equilibrium↗
PubMed1998

The application of an in vitro perfused liver preparation to examine the effects of epinephrine and bovine thyroid-stimulating hormone on triiodo-L-thyronine release from the liver of rainbow trout (Oncorhynchus mykiss).

An isolated, perfused rainbow trout liver preparation was developed to investigate the action of nonthyroidal hormones on hepatic thyroid hormone metabolism. Several assessments were made of the stability and viability of the preparations under a range of conditions, including measures of lactate dehydrogenase flux and tissue ATP and glycogen content, all of which indicated that the perfused liver was stable for the 60-min perfusion period. Moreover, the liver preparations were responsive to an epinephrine challenge and, throughout the series of experiments, sustained hepatic glucose release. Triiodo-L-thyronine (T3) flux from the liver preparation was significantly increased by the provision of thyroxine (T4) substrate. Epinephrine and bovine thyroid stimulating hormone (TSH) were perfused alone and in combination with T4 to evaluate the effect of these hormones on T3 flux from the liver. Both epinephrine and TSH significantly enhanced hepatic T3 flux in the absence of T3 substrate, but neither had an additional effect on T3 flux when perfused in combination with T4. The results of the study suggest that a relationship exists between the circulating levels of nonthyroid hormones and peripheral thyroid hormone metabolism that may be receptor-mediated.

Adenosine Triphosphate↗
PubMed1998

Endothelial and smooth muscle cell conduction in arterioles controlling blood flow.

We performed intracellular recording with Lucifer yellow dye microinjection to investigate the cellular pathway(s) by which constriction and dilation are conducted along the wall of arterioles (diameter 47 +/- 1 microns, n = 63) supplying blood flow to the cheek pouch of anesthetized hamsters. At rest, membrane potential (Em) of endothelial (-36 +/- 1 mV) and smooth muscle (-35 +/- 1 mV) cells was not different. Micropipette delivery of norepinephrine (NE) or phenylephrine (PE) produced smooth muscle cell depolarization (5-41 mV) and vasoconstriction (7-49 microns) at the site of release and along the arteriole with no effect on Em of endothelial cells. KCl produced conduction of depolarization and vasoconstriction with similar electrical kinetics in endothelial and smooth muscle cells. Acetylcholine triggered conduction of vasodilation (2-25 microns) and hyperpolarization (3-33 mV) along both cell layers; in smooth muscle, this change in Em was prolonged and followed by a transient depolarization. These cell-specific electrophysiological recordings uniquely illustrate that depolarization and constriction are initiated and conducted along smooth muscle, independent of the endothelium. Furthermore, conduction of vasodilation is explained by the spread of hyperpolarization along homologously coupled endothelial and smooth muscle cells, with distinctive responses between cell layers. The discontinuity between endothelium and smooth muscle indicates that these respective pathways are not electrically coupled during blood flow control.

Acetylcholine↗
PubMed1998

Oxygen induces electromechanical coupling in arteriolar smooth muscle cells: a role for L-type Ca2+ channels.

We tested whether O2-induced vasomotor responses of arterioles correspond to changes in membrane potential (Em) of cells in the arteriolar wall. The cheek pouches of anesthetized male hamsters were prepared for intravital microscopy and intracellular recording. Microelectrodes containing Lucifer yellow dye were used to label smooth muscle cells (SMC) or endothelial cells (EC) during arteriolar responses to O2. During low- PO2 superfusion (approximately 20 Torr; arteriolar diameter 55 +/- 2 micron), Em of SMC and EC averaged -37 and -36 mV, respectively. High-PO2 superfusion ( approximately 150 Torr) depolarized SMC (to -15 +/- 1 mV) with vasoconstriction (to 24 +/- 2 micron) and diameter cycled with Em of SMC during vasomotion. In contrast, the Em of EC did not change with PO2 nor during vasomotion, yet Em depolarized by 21 +/- 2 mV when the extracellular K+ concentration ([K+]o) was raised to 55 mM. Superfusion with diltiazem (10 microM) or nifedipine (1 microM) abolished vasomotor and electrical responses to PO2 in SMC but did not eliminate depolarizations to elevated [K+]o. We conclude that, under physiological conditions, electrical and mechanical responses of arteriolar SMC to changes in PO2 are mediated through L-type Ca2+ channels without corresponding electrical activity in EC.

Animals↗
PubMed1997

Metabolite accumulation increases adenine nucleotide degradation and decreases glycogenolysis in ischaemic rat skeletal muscle.

Adenine nucleotides and glycogen are degraded in skeletal muscle during no-flow ischaemia. Past investigations have ascribed these metabolic changes to the severe energetic stress which arises with the removal of exogenous substrates (principally oxygen). We tested this hypothesis by measuring the high-energy phosphagen and glycogen contents of stimulated rat hindlimb muscles (1 twitch s-1) prior to and following 40 min of no-flow ischaemia or hypoxic perfusion without glucose (PaO2 = 4.6 +/- 0.1 torr, plasma glucose = 0.3 +/- 0.1 mmol L-1). Both experimental protocols eliminated exogenous substrate supply; however, the maintenance of flow during hypoxic perfusion ensured the removal of metabolic by-products. A period of forty minutes of skeletal muscle ischaemia was characterized by reductions in the total adenine nucleotide pool, phosphocreatine and glycogen in the slow oxidative soleus, fast oxidative-glycolytic plantaris and the fast glycolytic white gastrocnemius. Compared to ischaemia, the total adenine nucleotide pool was higher (by 7.2-13.3 mumol g-1 dry wt) and the glycogen content lower (by 10.0-16.6 mumol g-1 dry wt) in skeletal muscle exposed to hypoxic perfusion without glucose. The ability of hypoxic perfusion to attenuate TAN degradation and augment glycogenolysis can be attributed to metabolic by-product removal. By limiting muscle lactate and PCO2 accumulation, hypoxic perfusion without glucose attenuates cellular acidification; this could in turn limit AMP deaminase activation and glycogen phosphorylase inhibition. We conclude that the ischaemia-induced alterations in adenine nucleotide and glycogen metabolism arise in response to the elimination of exogenous substrates and to the accumulation of metabolic by-products.

Adenine Nucleotides↗
PubMed1997

Coactivation of resistance vessels and muscle fibers with acetylcholine release from motor nerves.

Acetylcholine (ACh) released at the neuromuscular junction (NMJ) triggers muscle fiber contraction. We tested whether this source of ACh also triggers vasodilation. Arterioles [diameter: 4th order (4A), 18 +/- 3 microns; 2nd order (2A), 35 +/- 2 microns] and feed arteries (60 +/- 4 microns) were observed in retractor muscle of anesthetized hamsters. During stimulation [25% duty cycle (500-ms train, 1 per 2 s) at approximately 40% of maximum isometric tension], a nicotinic receptor antagonist (tubocurarine, 10 microM) prevented contraction, yet 2A and 4A arterioles and feed arteries rapidly (< or = 5 s) dilated (by 9 +/- 2, 11 +/- 3, and 8 +/- 1 microns, respectively; P < 0.05); neither cholinergic innervation of the vasculature nor ACh release from endothelium was apparent. Vasodilator responses doubled (P < 0.05) with cholinesterase inhibition (eserine, 1 microM) and were abolished with muscarinic receptor antagonism (atropine, 10 microM). Microiontophoresis of ACh onto arterioles triggered vasodilation that conducted into feed arteries, confirming functional continuity between intramuscular and extraparenchymal resistance vessels. To determine whether ACh served as a vasodilator during exercise, vascular responses to muscle contraction were measured in the presence or absence of atropine. With 2.5% duty cycle (50 ms, 1 per 2 s), atropine attenuated vasodilation by 35% in 2A and 51% in 4A arterioles and by 65% in feed arteries. With 25% duty cycle, arteriolar dilation was unaffected by atropine, yet feed artery dilation was attenuated by 60%; this was accompanied by a 50% reduction in functional hyperemia. Our findings indicate that ACh "spillover" from NMJs can coactivate muscarinic receptors, giving rise to a dilation that is conducted into feed arteries. This ascending vasodilation is integral to the full expression of functional hyperemia.

Acetylcholine↗
PubMed1996

L-type Ca2+ channel and Na+/Ca2+ exchange inhibitors reduce Ca2+ accumulation in reperfused skeletal muscle.

It is known that extracellular Ca2+ accumulates within skeletal muscle after prolonged periods of ischemia and reperfusion. In this study, we determined whether the L-type Ca2+ channel and the Na+/Ca2+ exchanger mediated Ca2+ influx and whether Ca2+ accumulation limited the metabolic and contractile recovery of reperfused skeletal muscle. Contracting rat hindlimbs (1-Hz twitch) exposed to 40 min of no-flow ischemia were reperfused with diltiazem (500 microM) or 3,4-dichlorobenzamil (300 microM) to block the Na+/Ca2+ exchanger and/or the L-type Ca2+ channel. High inhibitor concentrations were used to counter the binding of diltiazem and 3,4-dichlorobenzamil to albumin and red blood cells. Muscle Ca2+ accumulation, contractile function, and energy metabolism were assessed by measuring intracellular Ca2+ concentration ([Ca2+]i), Ca2+ influx, twitch tension, and high-energy phosphagens [ATP, total adenine nucleotides (TAN) and phosphocreatine (PCr)]. Compared with control reperfusion, diltiazem and 3,4-dichlorobenzamil reduced Ca2+ influx and attenuated the rise in [Ca2+]i in the fast-oxidative glycolytic plantaris (Pl) and the fast-glycolytic white gastrocnemius (WG). The inhibitor-induced decrease in Ca2+ influx was 1.5- to 2-fold greater with 3,4-dichlorobenzamil than with diltiazem. Coinciding with the reduced Ca2+ accumulation, diltiazem and 3,4-dichlorobenzamil enhanced the resynthesis of ATP (Pl and WG), PCr (Pl and WG), and TAN (Pl) compared with control reperfusion. 3,4-Dichlorobenzamil also augmented twitch-tension recovery. We conclude that Ca2+ accumulation during reperfusion 1) arises from L-type Ca2+ channel and Na+/Ca2+ exchange activation; and 2) impairs the metabolic and contractile recovery of skeletal muscle.

Adenosine Triphosphate↗
PubMed1996

Muscle length directs sympathetic nerve activity and vasomotor tone in resistance vessels of hamster retractor.

Increased resistance to blood flow with muscle extension has been explained by the deformation of vessels within the muscle. In the present study, we developed a novel preparation of the hamster retractor muscle to investigate whether passive changes in skeletal muscle length elicit active vasomotor responses through a range of motion (85% to 130% of in vivo length; sarcomere length, 2.69 +/- 0.02 to 4.05 +/- 0.01 microns) encompassing the classic length-tension relationship. Arterioles (diameter, 32 +/- 3 microns) and feed arteries (diameter, 75 +/- 4 microns) were observed to progressively constrict (by 8 +/- 1 and 17 +/- 2 microns, respectively) with muscle lengthening, reducing blood flow by > 50%; reciprocal changes occurred with passive shortening. Sodium nitroprusside (10 mumol/L) dilated vessels (to 47 +/- 2 and 98 +/- 4 microns, respectively) and abolished vasomotor responses to changing muscle length. The coordination of vasomotor responses between arterioles and feed arteries maintained wall shear rate (control, 1764 +/- 200 s-1) and perfusion pressure (60 +/- 5 mm Hg) into the arteriolar network. Tetrodotoxin (TTX, 1 mumol/L), phentolamine (1 mumol/L), prazosin (0.1 mumol/L), or 6-hydroxydopamine (1 mmol/L) inhibited vasoconstrictor responses, indicating that action potentials initiated by muscle lengthening give rise to norepinephrine release from sympathetic nerves. As shown with glyoxylic acid staining, sympathetic nerves formed a plexus encompassing arterioles and feed arteries. To test for a reflexive response initiated by intramuscular mechanoreceptors, TTX was applied with micropipettes to proximal segments of feed arteries, thereby neurally "isolating" the muscle from the hamster. Whereas lengthening-induced vasoconstriction persisted in arterioles and in feed artery segments distal to TTX, there was no vasomotor response central to the block. We conclude that passive lengthening stimulates the activity of periarteriolar sympathetic nerves; this activity propagates antidromically along nerve fibers into the feed arteries. These findings identify a mechanotransduction sequence by which the length of skeletal muscle actively governs vasomotor tone and the supply of oxygen to muscle fibers.

Animals↗
PubMed1993

Energy metabolism and adenine nucleotide degradation in twitch-stimulated rat hindlimb during ischemia-reperfusion.

The purpose of this study was to characterize twitch tension and energy metabolism in ischemic, stimulated rat hindlimb to determine its suitability as a rapid time course model of ischemia-reperfusion injury. After 15 min equilibration, rat hindlimbs were stimulated (1-Hz twitches, 0.2 ms pulse duration, 15 V) for 5 min (control, n = 8). This twitch protocol was maintained throughout the ischemic and reperfusion periods. The control period was followed by 5, 20, or 40 min of ischemia (ligation of femoral artery and vein) or 40 min of ischemia with 0, 5, or 20 min of reperfusion (removal of ligature). The soleus [89% slow oxidative (SO)] and the white gastrocnemius [WG; 91% fast glycolytic (FG)] were analyzed for phosphocreatine (PCr), adenine nucleotides, glycogen, and glycolytic intermediates. Ischemia was characterized by progressive decreases in twitch tension, high-energy phosphagens, total adenine nucleotides (TAN), and glycogen. Also, energy metabolism was altered at a greater rate in WG than in soleus. Reperfusion resulted in a recovery in PCr and lactate, with little change in ATP, TAN, or glycogen. The inability to resynthesize adenine nucleotides and glycogen during reperfusion is characteristic of damaged skeletal muscle. The extent of the metabolic alterations in SO and FG muscles during twitch stimulation was comparable with previously reported noncontracting ischemia protocols of 2-4 and 4-7 h in length, respectively. The present study demonstrates that twitch stimulation of ischemic skeletal muscle is a useful model for inducing rapid metabolic changes and an ischemic insult comparable to prolonged noncontracting ischemia-reperfusion models.

Adenine Nucleotides↗