Analysis of free inositol trisphosphate in heart tissue by FPLC and isotachophoresis

Effects of adrenergic and muscarinic agonist stimulation on IP3 and cyclic nucleotide levels in the pressure overloaded rat heart

In this study, the dynamic interrelationships between myocardial functional state and changes in the second messenger content in pressure-overloaded hypertrophied hearts were investigated. Forty-three rat hearts were used after partial clamping of the abdominal aorta. The isolated hearts were perfused with Krebs-Henseleit buffer and allocated to perfusion for 20 s or 40 min as controls (n = 12); or with noradrenaline (10(-6) mol l-1, n = 11); carbachol (3 x 10(-7) mol l-1, n = 9); or noradrenaline plus carbachol (10(-6) mol l-1 + 3 x 10(-7) mol l-1, respectively, n = 11). maxdP/dt increased more than 2-fold already after 20 s on noradrenaline stimulation, followed by a significant increase in cAMP. After 40 min, maxdP/dt was lower than the maximal value, although higher than controls. cAMP was also decreased, but still significantly higher than controls. Perfusion with noradrenaline plus carbachol produced the same changes in maxdP/dt as those seen after noradrenaline stimulation alone, but failed to increase cAMP content after both 20 s and 40 min. The inositol trisphosphate (IP3) content was increased 40 min of control perfusion (p < 0.05). Noradrenaline and carbachol, separately, produced an increase in IP3 content already after 20 s (p < 0.05). The combination of noradrenaline plus carbachol also produced an increase of IP3 (p < 0.05; compared to controls), but to a lesser extent when compared either to noradrenaline or carbachol (p < 0.05). After 40 min of perfusion, IP3 was in the same range regardless of added agonist(s) and still slightly above control level (p < 0.05). The early increase in maxdP/dt induced by noradrenaline or the combination of noradrenaline plus carbachol was not paralleled by a decrease in ATP content. This was also the case upon addition of carbachol alone. However, after 40 min of agonistic perfusion, ATP levels were substantially decreased. In conclusion, myocardial IP3 content in pressure-overloaded hypertrophied hearts was not different from that of sham-operated hearts. After agonistic stimulation, an early increase in IP3 formation was seen. Attenuation of the IP3 response by combined stimulation with noradrenaline and carbachol was initially present in pressure-overloaded hypertrophied hearts. After 40 min no attenuation was found for either IP3 or for cAMP content, suggestive of induction of a desensitization.

Inositol-1,4,5-trisphosphate mass content in isolated perfused rat heart during alpha-1-adrenoceptor stimulation

Inositol-1,4,5-trisphosphate (IP3) has been proposed to be a second messenger in response to alpha-1-adrenoceptor stimulation also in myocardial cells. We studied the effect of alpha-1-adrenoceptor stimulation (5 x 10(-5) mol/l phenylephrine or 5 x 10(-5) mol/l noradrenaline both in the presence of 10(-6) mol/l timolol) on IP3 mass content in isolated perfused rat hearts. IP3 content was determined by a specific receptor-binding assay-kit (TRK 1000, Amersham) after validating the method. For comparison also the effect of muscarinic stimulation (10(-4) mol/l carbachol in the presence of 10(-6) mol/l timolol) on IP3 content was measured in corresponding preparations. A basal IP3 level of about 75 pmol/mg protein was found. There were no prominent effects of alpha-1-adrenoceptor stimulation on total IP3 content in isolated perfused rat hearts. Phenylephrine gave a statistically significant increase of about 40% at 1/4 min and a statistically significant decrease of about 25% at 4 min after start of exposure. Noradrenaline, however, gave no statistically significant change of IP3 at the time-points studied. Muscarinic stimulation caused a slight, statistically insignificant, increase of IP3 at 1/4 min. The results are compatible with an assumption that agonist stimulation evokes a localized increase of IP3 which may be masked by a relatively high total IP3 mass content. The IP3 peak after phenylephrine coincided with the early positive inotropic phase of the response reported earlier in perfused rat hearts for alpha-1-adrenoceptor stimulation by phenylephrine. Although this might be compatible with a role for IP3 in this early and transient phase, a mediator function of IP3 in the inotropic response is not established.

Myocardial contractile response and IP3, cAMP and cGMP interrelationships

An experimental study in the perfused working normal and pressure overloaded rat heart. A mini review based on a doctoral thesis.

Myocardial inositoltrisphosphate is depressed by dibutyryl cAMP. An experimental study in the isolated working rat heart

A possible interrelation between IP3 and cAMP was studied in rat myocardium through circumvention of the receptor mediated stimulatory step of adenylyl cyclase by the administration of dibutyryl cAMP (db-cAMP). Changes in IP3 and cyclic nucleotide contents were correlated to changes in contractility after 40 min of beta- and alpha-adrenergic stimulation. Rat hearts (n = 23) were perfused with Krebs-Henseleit buffer in a modified Langendorff apparatus as a working preparation. The hearts were allocated to perfusion as control (n = 6); or with phenylephrine (10(-6) mol L-1, n = 6); (-)-isoproterenol (10(-6) mol L-1, n = 6); db-cAMP (2 x 10(-4) mol L-1, n = 5). All hearts were freeze-clamped after 40 min of perfusion. Phenylephrine produced a slow increase in maxdP/dt reaching a maximal value after 10 min (P < 0.05); thereafter it decreased, reaching the control level at 30 min. Isoproterenol perfusion resulted in an early (20 s) increase in maxdP/dt (P < 0.05). Over the next 10s maxdP/dt decreased markedly reaching an inflection point at 30 s. Thereafter only a slow increase during the rest of the perfusion was seen. Dibutyryl cAMP increased maxdP/dt slowly during the whole perfusion period reaching maximum after 40 min. Cyclic-AMP was increased by 21% after 40 min of phenylephrine perfusion while the corresponding increases by isoproterenol and db-cAMP were 131 and 105%, respectively (P < 0.05). Phenylephrine increased IP3 content to the same extent as isoproterenol perfusion (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Carbachol-induced increase in inositol trisphosphate (IP3) content is attenuated by adrenergic stimulation in the isolated working rat heart

The interrelated responses of concomitant adrenergic and muscarinic receptor stimulation on second messengers and mechanical activity in the isolated perfused working rat heart were studied. The hearts were perfused with Krebs-Henseleit buffer in a modified Langendorff apparatus. The hearts were perfused with noradrenaline (10(-6) mol L-1, n = 20), with carbachol (3 x 10(-7) mol L-1, n = 11) or with noradrenaline plus carbachol (n = 20) in the above-mentioned concentrations. The hearts were frozen at 20 s, 30 s and 40 min after addition of noradrenaline and noradrenaline plus carbachol and at 20 s and 40 min after addition of carbachol. Five hearts were freeze-clamped directly after preperfusion and another five hearts after 40 min of perfusion and used as controls. Myocardial cAMP increased at 20 s and 40 min after noradrenaline perfusion. In contrast to this cAMP was unchanged at 20 s and decreased at 40 min after perfusion with noradrenaline plus carbachol. IP3 content increased after 20 s of carbachol- and after 40 min of noradrenaline perfusion (P < 0.05). However, noradrenaline plus carbachol did not induced any significant increase in IP3 content after 20 s and 30 s, but after 40 min a decrease below basal level was found (P < 0.05). Noradrenaline stimulation attenuated muscarinic agonist induced IP3 formation. A reciprocity existed in that noradrenaline induced IP3 formation was attenuated by carbachol. No direct relationship was observed between the IP3 response and contractility, also valid for cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamic changes of myocardial inositoltrisphosphate and cyclic nucleotides: relationship to contractile response in the perfused working rat heart after adrenergic and muscarinic agonist stimulation

Initial and late effects by adrenergic and muscarinic agonists on inositol trisphosphate (IP3) and cyclic nucleotide levels were determined and correlated to mechanical response in perfused rat hearts. Forty-three rat hearts were perfused with Krebs-Henseleit buffer in a modified Langendorff apparatus as a working preparation. The hearts were perfused as controls (n = 11), or with noradrenaline (10(-6) mol l-1) (n = 21), or with carbachol (3 x 10(-7) mol l-1) (n = 11) added to the perfusion buffer. The hearts were frozen at 20 s, 30 s and 40 min after addition of noradrenaline and at 20 s and 40 min after addition of carbachol, and after 5 and 45 min of control perfusion. cAMP and cGMP were determined by radioligand methods and IP3 by a combined fast performance liquid chromatography (FPLC)-isotachophoretic method. cAMP increased by 36% within 20 s followed by a decrease (22%) during the 10 s following noradrenaline addition. After 40 min cAMP regained its value near that of 20 s. Noradrenaline perfusion did not influence IP3 levels during the first 30 s although the value at 40 min was significantly higher (59%). IP3 increased (42%) after 20 s of carbachol perfusion followed by a 25% decrease at 40 min. Sustained stimulation of beta-receptors (after 40 min in our model) resulted in a repeated increase in cAMP only, without an increase in contractility.(ABSTRACT TRUNCATED AT 250 WORDS)

Innovative developments in isotachophoresis (displacement electrophoresis)

This Mini Review is aimed at characterizing the innovative developments in isotachophoresis (ITP) during the past few years, discussing in turn new theoretical, analytical, preparative and applicative aspects of this unique separation method. Examples given from our laboratory include the study of the detailed dynamics of the ITP separation of four components by computer simulation and experimental validation in a capillary-type instrument with multiple sensors along the separation trough; the anionic ITP analysis in presence of a strong cathodic electroosmotic flow using an open-tubular fused-silica capillary with on-column multiwavelength detection, and the fractionation of proteins in a screen-segmented, rotating column as well as by recycling ITP.