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N Deutsch

Publications and source records attributed to N Deutsch.

9 recordsLinked to original sources
PubMed1998

Lysophosphatidylcholine and Cellular Potassium Loss in Isolated Rabbit Ventricle.

BACKGROUND: Lysophospholipids such as lysophosphatidylcholine (LPC) have many direct electrophysiological effects on cardiac muscle and have been implicated as a cause of lethal ventricular arrhythmias during acute myocardial ischemia. Because extracellular K(+) accumulation is also a key arrhythmogenic factor during acute ischemia, we examined the effects of LPC on cellular K(+) balance, including its interaction with adenosine triphosphate-sensitive K(+) (K(ATP)) channels. METHODS AND RESULTS: Isolated rabbit interventricular septa paced at 75 beats/min were loaded with (42)K(+) to measure unidirectional K(+) efflux rate (in (42)K(+) washout experiments) or tissue K(+) content ((42)K(+) uptake experiments) and action potential duration (APD) during exposure to 20 µM LPC for 30 minutes. LPC caused tissue K(+) content to decrease by 15 +/- 2% (n = 4) at a steady rate over 30 minutes, associated with gradual APD shortening and a delayed increase in unidirectional K(+) efflux rate. Pretreatment with 12 µM cromakalim to selectively activate K(ATP) channels shortened APD by 44 +/- 66% and had no effect on net tissue K(+) content during control aerobic perfusion. However, cromakalim increased net K(+) loss during exposure to LPC to 22 +/- 4%, a 47% increase. CONCLUSIONS: LPC induced net K(+) loss in heart, which was potentiated by the K(ATP) channel agonist cromakalim. This ATP finding suggests that if LPC accumulates to similar levels during myocardial ischemia and hypoxia, it may be an important mechanism in net K(+) loss.

Journal Article↗
PubMed1994

Surface charge and properties of cardiac ATP-sensitive K+ channels.

ATP-sensitive K+ (KATP) channels are present in a wide variety of tissues. The sensitivity of these channels to closure by cytosolic ATP (ATPi) varies significantly among different tissues and even within the same tissue. The purpose of this study was to test the hypothesis that negative surface charges modulate the sensitivity of the KATP channels to ATPi by influencing surface potential in the vicinity of the ATP-binding site(s) of the channel. Unitary currents through KATP channels were measured in inside-out membrane patches excised from rabbit ventricular myocytes using the patch-clamp technique. Agents known to be effective at screening negative surface charges were applied to the cytosolic surface of the patches, and their effects on ATP sensitivity were examined. These agents included Mg2+ (2-15 mM), Ba2+ (2-10 mM), and the polycations protamine (0.01-10 microM), poly-L-lysine (500 microM), and poly-L-arginine (0.5 microM). The divalent cations and the various polycations all dramatically reduced the concentration of ATPi required to half-maximally suppress current through KATP channels (Kd), from approximately 100 microM in the absence of these agents to 1.6-8 microM in their presence. The effects were dose dependent. Protamine also reduced the sensitivity of KATP channels to block by cytosolic ADP. The sensitivity of KATP channels to block by ATP was independent of membrane potential, suggesting that the ATP-binding site is not located within the transmembrane voltage field. The effects of the polycation poly-L-lysine on ATP sensitivity were also independent of membrane potential or the direction (inward or outward) of current through KATP channels. In addition to increasing ATP sensitivity, Mg2+, Ba2+, and the polycations all caused dose-dependent block of inward and outward currents through KATP channels over similar concentration ranges as their effects on ATP sensitivity. The block of inward current by polycations was not associated with reduction of single-channel conductance or evidence of fast open channel block. However, the polycations did cause a modest reduction in single-channel conductance of outward current. These results are consistent with the presence of negative surface charges that reduce the local ATP concentration at the ATP-binding site(s) on the channel, relative to the bulk cytosolic ATP concentration. Screening these negative surface charges with divalent cations or polycations decreases the local ATP gradient, resulting in a decrease in the apparent Kd for ATP.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Diphosphate↗
PubMed1994

Effects of trypsin on cardiac ATP-sensitive K+ channels.

Treatment with trypsin of the cytoplasmic surface of excised inside-out membrane patches from guinea pig ventricular myocytes altered multiple regulatory properties of ATP-sensitive K+ (KATP) channels including their sensitivity to intracellular ATP (ATPi), intracellular ADP (ADPi), glibenclamide, and cromakalim. The single-channel conductance, reversal potential, and inward rectification (in the presence of intracellular Mg2+) were unaltered after trypsin treatment. KATP channels also remained sensitive to intracellular Ca(2+)-induced rundown after trypsin treatment (n = 6). The effects of trypsin were not prevented by including either 15 mM ATPi (n = 7), 1 mM ADPi (n = 4), or 10 microM glibenclamide (n = 4) during exposure to trypsin, suggesting that occupancy of these binding sites did not prevent access of trypsin to the proteolytic sites responsible for its effects. Treatment of excised membrane patches with 1 mM phenylglyoxal (n = 4) or 5 mM glyoxal (n = 4), which cleave polypeptides at arginine residues, did not increase the dissociation constant for suppression of KATP channels by ATPi. Because trypsin cleaves peptides at both arginine and lysine residues, these results suggest that modification of the regulatory properties of KATP channels by trypsin may result from proteolytic digestion of lysine residues located in cytosolic regions of the channel protein.

Adenosine Diphosphate↗
PubMed1993

ATP-sensitive K+ channel modification by metabolic inhibition in isolated guinea-pig ventricular myocytes.

1. ATP-sensitive K+ (K+ATP) channels are believed to make an important contribution to the increased cellular K+ efflux and shortening of the action potential duration (APD) during metabolic inhibition, hypoxia, and ischaemia in the heart. The mechanisms by which the activity of the K+ATP channel is regulated during conditions of metabolic impairment are not completely clear. Extrinsic factors such as increased [ADP]i, acidosis, and stimulation of adenosine receptors appear to decrease the K+ATP channel's sensitivity to closure by [ATP]i. The purpose of this study was to determine whether the K+ATP channel itself is intrinsically altered by the processes associated with metabolic impairment. 2. Isolated guinea-pig ventricular myocytes were metabolically inhibited in glucose-free 1.8 mM Ca2+ Tyrode solution containing 9 microM rotenone and 0.9 microM carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP) while recording unitary currents through K+ATP channels in cell-attached patches. When K+ATP channel activity became maximal, the patch was excised (inside-out) into 150 mM K+ bath solution containing different ATP concentrations. The Kd for suppression by [ATP]i ([ATP]i causing half-maximal suppression of current through K+ATP channels) was markedly increased to 305 microM (n = 9) compared to patches excised from control myocytes not exposed to metabolic inhibitors (Kd = 46 microM, n = 28). 3. A [Ca2+]i-dependent process was involved in K+ATP channel modification during metabolic inhibition. Removal of extracellular Ca2+ during metabolic inhibition led to an intermediate decrease in the ATP sensitivity of the K+ATP channels (Kd = 120 microM, n = 6). In myocytes that were pretreated with 10 microM ryanodine in addition to removing extracellular Ca2+, the reduction in ATP sensitivity was completely prevented (Kd = 23 microM, n = 6). 4. In inside-out membrane patches excised from control non-metabolically inhibited myocytes, elevated free [Ca2+]i (2 microM) did not alter the sensitivity of the K+ATP channel to closure by [ATP]i, suggesting that in metabolically inhibited myocytes elevated [Ca2+]i acted indirectly. K+ATP channel run-down was found to increase the sensitivity of K+ATP channels to closure to [ATP]i (Kd = 16 microM, n = 13). 5. Inside-out membrane patches excised from control non-metabolically inhibited myocytes were also exposed to various proteases, phospholipases and other reagents that may be activated during metabolic inhibition. Trypsin and chymotrypsin treatment increased the Kd from 39 to 213 microM (n = 8) and 110 microM (n = 5), respectively. Calpain I had no apparent effect on the Kd.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1991

Activation of cardiac ATP-sensitive K+ current during hypoxia: correlation with tissue ATP levels.

Although previous work has implicated activation of ATP-sensitive K+ currents (IK,ATP) in action potential duration (APD) shortening and increased cellular K+ efflux during hypoxia, ischemia, and metabolic inhibition, no prior study has directly assessed the tissue levels of ATP at which IK,ATP activates in intact cardiac muscle. Accordingly, we correlated changes in tissue high-energy phosphate levels during substrate-free hypoxia with activation of IK,ATP in intact voltage-clamped rabbit papillary muscles. During 10 min of hypoxia, the outward K+ current measured in response to a voltage-clamp pulse step from -50 to 0 mV increased from 8.57 +/- 0.27 to 15.67 +/- 1.41 microA (P less than 0.05, n = 6), and APD decreased from 452 +/- 54 to 292 +/- 56 ms (P less than 0.05, n = 6). Glibenclamide (10 microM), a specific IK,ATP blocker, prevented both of these changes. In a parallel set of experiments, papillary muscles were freeze-clamped and assayed for tissue ATP. In these muscles, 10 min of hypoxia resulted in a comparable degree of APD shortening (441 +/- 24 to 297 +/- 18 ms, P less than 0.05, n = 12), and tissue ATP levels fell from 13.2 +/- 1.3 to 9.7 +/- 0.7 mumol/g dry wt (P less than 0.05, n = 12). These results directly demonstrate that IK,ATP is activated and causes APD shortening during hypoxia in intact cardiac muscle despite only a modest (approximately 25%) decline in tissue ATP content.

Action Potentials↗
PubMed1990

Suppression of ventricular arrhythmias by volatile anesthetics in a canine model of chronic myocardial infarction.

Ventricular tachycardia likely secondary to a reentrant mechanism may be reliably induced by programmed electrical stimulation in dogs 4-6 days after creating a 2-h experimental, occlusion-reperfusion myocardial infarction. The effects of 1.1 and 1.8 MAC halothane, isoflurane, and enflurane on pacing-induced arrhythmias were studied in this model. The ease of initiation of ventricular tachycardia was measured in both awake and anesthetized dogs (n = 18). Excitation thresholds, conduction times, and refractory periods in both normal and infarcted myocardium were also determined to understand changes in the ease of induction of the arrhythmias secondary to anesthetic exposure. Halothane and enflurane administration suppressed the induction of ventricular tachycardia compared with the unanesthetized control (P less than 0.01 for both). During isoflurane anesthesia, there was a trend that was not statistically significant for pacing-induced ventricular tachycardia to be less frequent than during the conscious state (P = 0.11). Halothane and enflurane prolonged refractory periods in both normal and infarcted myocardium, whereas isoflurane had that effect only in normal myocardium. In addition, halothane and enflurane tended to increase refractory periods more than isoflurane in both regions. Conduction times and excitation thresholds were not altered by anesthetic administration. It is concluded that halothane and enflurane suppress inducible ventricular arrhythmias secondary to a prior myocardial infarction. In addition, the increased efficacy of halothane and enflurane as antiarrhythmic agents compared with isoflurane in this model may be related to their greater prolongation of refractory periods.

Anesthetics↗