Acute partial sympathetic blockade by reserpine in the isolated rabbits' hearts

Modulation by nicotine of the ionic currents in guinea pig ventricular cardiomyocytes. Relatively higher sensitivity to IKr and IKl

The effects of nicotine on the ionic currents in guinea pig cardiomyocytes were investigated using a whole-cell voltage-clamp technique. Nicotine (30 microM to 1 mM) inhibited the ionic currents in a concentration-dependent manner. Nicotine at 30 microM did not affect the Ca2+ current (ICa), but at 300 microM inhibited ICa at 10 mV by 29.3 +/- 2.4% (n = 6, P < .01) and at 1 mM almost blocked the ICa (by approximately 90%, n = 5, P < .001). After 5- to 10-min washout, these responses had 50-70% recovery. The fast time constant (tau f) of the inactivation phase for ICa at 10 mV was not affected, but the slow one (tau s) increased from 35.7 +/- 2.8 to 39.5 +/- 2.4 ms (n = 7) at 300 microM nicotine. Nicotine at 100 microM also inhibited the delayed rectifier K+ current (IK) at 60 mV by 42.7 +/- 3.0% (n = 7, P < .01), and at 30 microM inhibited the inwardly rectifying K+ current (IKl) at -110 mV by 43.0 +/- 2.5% (n = 7, P < .01). The responses to nicotine were not significantly modified by atropine, hexamethonium, and nicotine receptor antagonists (d-tubocurarine and benzoquinonium). The IK is composed of two components for rapidly and slowly activated currents (IKr and IKs). Nicotine markedly decreased the tail current of IKr, but had less or no effect on that of IKs. However, the activation and inactivation kinetics (d infinity and f infinity) for ICa and its activation kinetics (P infinity) for IKr and IKs were not modified. These results suggest that nicotine inhibits the ionic currents with relatively higher sensitivity to IKl and IKr, resulting in modulation of the cardiac functions.

Effects of nicotine on spontaneous activity and underlying ionic currents in rabbit sinoatrial nodal cells

1. Effects of nicotine on the spontaneous action potentials and the underlying ionic currents in rabbit sinoatrial (SA) nodal cells were investigated using current-clamp and whole-cell voltage-clamp modes. 2. Nicotine (30 microM to 1 mM) produced a negative chronotropic effect in a concentration-dependent manner (at 1 mM by 10.6 +/- 2.8%, n = 9, p < 0.01). Nicotine at 300 microM significantly decreased the maximum rate of depolarization by 9.8 +/- 1.3% (n = 9, p < 0.05). Other action potential parameters were not affected to any significant extent. 3. Pretreatment with atropine (1 microM) and hexamethonium (1 mM) did not modify the nicotine-induced effects. After washout, these responses were reversible. 4. Isoprenaline decreased the responses induced by nicotine, but ACh increased them. 5. Nicotine at 100 microM did not affect the L-type Ca2+ current (ICa), but at 300 microM inhibited it at + 10 mV by 21.6 +/- 2.9% (n = 6, p < 0.05). The fast time constant (tau f) of the inactivation phase for ICa was not affected, but the slow one (tau s) significantly increased from 36.8 +/- 1.9 ms to 41.2 +/- 2.8 ms (n = 6) at 300 microM nicotine. The activation and inactivation kinetics (d infinity and f infinity) for ICa were not modified. 6. Nicotine also did not affect the delayed rectifier K+ current (IK) and its activation kinetic (P infinity). 7. These results suggest that nicotine depresses the action potentials and causes a negative chronotropic effect due to inhibitions of the ionic currents in the SA nodal cells.

Negative chronotropic and inotropic responses to nicotine in rat right and left atria

1. Comparison between the chronotropic and inotropic effects induced by nicotine in the right and left atrial muscles of rat was investigated. 2. Nicotine (300 microM and 1 mM) significantly produced negative chronotropic and inotropic effects in the right atrium. The effects were concentration-dependent, and reached a maximum about 30 sec after nicotine administration (1 mM). The responses were attenuated with time even during exposure to nicotine (desensitization). 3. In the left atrium, nicotine (300 microM and 1 mM) caused a negative inotropic effect. The depression was decreased with an increase in the frequencies of stimulation (1-3 Hz). The negative inotropic effect reached a maximum at approx. 60 sec later. 4. Nicotine (1 mM) caused a greater negative inotropic response in the right atrium than in the left atrium by 23% (stimulated at 3 Hz). The effects were not modified by atropine (1 microM) and hexamethonium (1 mM). 5. There was no difference between single and cumulative administrations of nicotine in both right and left atrial muscles. 6. These results suggest that the negative chronotropic and inotropic effects of nicotine may be due mainly to a direct action on the cell membrane of rat atria, accompanied with down regulation of nicotinic ACh receptors. The difference between the right and left atria could result from a different innervation of the autonomic nervous system.

Reserpine inhibits rat anterior pituitary hormone secretion in vitro: effects on prolactin and ACTH and ultrastructural observations

We measured [3H]prolactin ([3H]Prl) synthesis and secretion in female rat anterior hemipituitary glands incubated in vitro, and immunoassayable Prl secretion from dispersed anterior pituitary cells in a perfused column. Anterior pituitary glands which were incubated in 9 microM reserpine showed a marked inhibition of [3H]Prl secretion but no change in hormone synthesis, thus causing [3H]Prl accumulation within the gland. The same concentration of reserpine produced a similar effect in pituitary glands taken from rats depleted of dopamine with alpha-methyl-p-tyrosine. Reserpine inhibited Prl secretion from dispersed anterior pituitary cells with a gradual onset and prolonged duration. Thyrotropin-releasing hormone (TRH), but not dibutyryl cyclic AMP (dbcAMP), the calcium ionophore A23187 or excess Ca2+, stimulated both [3H]Prl and Prl secretion in the presence of reserpine. In contrast, neither basal nor vasopressin-stimulated ACTH (bio- and immunoassayable) secretion was inhibited by 9 microM reserpine. Ultrastructurally, pituitary glands incubated in reserpine had an increased content of Prl secretory granules. Reserpine thus selectively inhibited Prl secretion, secondarily causing accumulation of both measurable hormone and Prl secretory granules within the pituitary gland. We hypothesize that reserpine interrupted calcium-dependent mechanisms in the stimulus-secretion coupling process to inhibit Prl release.