Reserpine, a competitive inhibitor of catecholamine transport into adrenal medullary chromaffin vesicles, consists of a trimethoxybenzoyl group esterified to an alkaloid ring system. Reserpine inhibits norepinephrine transport with a Ki of approximately 1 nM and binds to chromaffin-vesicle membranes with a KD of about the same value. Methyl reserpate and reserpinediol, derivatives that incorporate the alkaloid ring system, also competitively inhibit norepinephrine transport into chromaffin vesicles with Ki values of 38 +/- 10 nM and 440 +/- 240 nM, respectively. Similar concentrations inhibit [3H]reserpine binding to chromaffin-vesicle membranes. 3,4,5-Trimethoxybenzyl alcohol and 3,4,5-trimethoxybenzoic acid, derivatives of the other part of the reserpine molecule, do not inhibit either norepinephrine transport or [3H]reserpine binding at concentrations up to 100 microM. Moreover, trimethoxybenzyl alcohol does not potentiate the inhibitory action of methyl reserpate. Therefore, the amine binding site of the catecholamine transporter appears to bind the alkaloid ring system of reserpine rather than the trimethoxybenzoyl moiety. The more potent inhibitors are more hydrophobic compounds, suggesting that the reserpine binding site is hydrophobic.

An analysis of the subcellular localization of platinum was conducted in Sprague-Dawley (SD) rats following administration of an i.v. dose of 6 mg/kg cisplatin (bolus and infusion). Biodistribution studies were carried out in the liver and kidney of control animals, as well as in these same organs and in the tumor (Walker 256 adenocarcinoma) of SD rats. The results obtained illustrate that in addition to the platination of DNA in these tissues, significant amounts of Pt are also incorporated into the chromosomal protein (CP) and cytosolic fractions. The localization of Pt in the cytosolic fractions was highest in the kidney, followed by the tumor, and lowest in the liver when determined as the fractional percentage of the total amount of injected drug (%ID/g). The significance of such cytosolic and CP localization of Pt is not known at this time, but they may be involved in the cytotoxic effects of cisplatin, as this drug is cytotoxic to tumors and kidneys but not to the liver. The localization of cisplatin in the subcellular fractions of liver, kidney, and tumor showed a trend toward being higher after i.v. infusion than after i.v. bolus administration of the drug.

Acetylcholine (ACh) causes contraction of Aplysia buccal muscles E1 and I5, and serotonin (5-hydroxytryptamine, 5-HT) enhances ACh-elicited contractions of these muscles. Possible roles of calcium influx in mediating these responses were examined by studying influx of 45Ca++. 5-HT increased calcium influx into both I5 and E1. Maximal influx occurred at 10(-6) M 5-HT and the increased influx could be sustained in the presence of 5-HT for at least 10 min. ACh also caused calcium influx, and calcium influx increased approximately in proportion to log[ACh] from 10(-5) M to 10(-3) M ACh. 5-HT and ACh probably bring about calcium influx by different mechanisms since the effect of ACh was additive to a maximal 5-HT response, and 10(-4) M hexamethonium bromide inhibited the increased influx caused by ACh but did not affect influx caused by 5-HT. Cyclic AMP analogues and forskolin neither caused an increase in calcium influx nor an increase in the influx caused by ACh. The data support a model in which ACh-elicited contractions of I5 and E1 are due primarily to calcium entry across the extracellular membrane, and 5-HT can "load" an intracellular site by a mechanism different from that activated by ACh. The data do not support a role for cyclic AMP in mediating the calcium influx response to 5-HT.

Serotonin [5-hydroxytryptamine (5-HT)] enhances acetyl choline (ACh)-elicited contractures of Aplysia buccal muscles E1 and I5 . The possible role of external calcium in regulating the magnitude of ACh contracture in the presence and absence of 5-HT was investigated. Superfusion of E1 with zero calcium medium caused ACh contractures to fail within one to two minutes. Recovery of ACh contracture upon restoring normal medium occurred within two to four minutes. In the absence of 5-HT, ACh contracture decreased proportionally to external [Ca++] in the concentration range of 0-10 mM; however, the amount of enhancement of ACh contracture following 5-HT treatment did not decrease with external [Ca++] as long as [Ca++] was above a threshold concentration that varied from preparation to preparation. For most preparations, the enhancement of ACh contracture by 5-HT was dependent on the presence of external calcium during 5-HT treatment. Calcium influx into muscles E1 and I5 increased approximately two and a half fold in the presence of 10(-6) M 5-HT. A model in which 5-HT brings about calcium "loading" of an ACh releasable intracellular storage site is discussed.

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