1H-NMR studies of calmodulin: the modifying effect of W-7 (N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide) on the calcium-induced conformational changes of calmodulin

Regulation of blood pressure with calcium-dependent dopamine synthesizing system in the brain and its related phenomena

The effects of calcium on blood pressure regulation remain controversial. Although the mechanism by which calcium increases blood pressure when it is given intravenously and acutely has been elucidated, that by which calcium reduces blood pressure when it is supplemented chronically and slightly through daily diet is unclear. From a number of animal experiments concerning the effects of calcium on blood pressure, we believe that calcium ions have two separate roles in the regulation of blood pressure through both central and peripheral systems: (1) calcium ions reduce blood pressure through a central, calcium/calmodulin-dependent dopamine-synthesizing system and (2) calcium ions increase blood pressure through an intracellular, calcium-dependent mechanism in the peripheral vasculature. These concepts were applied to elucidate the mechanisms underlying hypertension in spontaneously hypertensive rats (SHR) and changes in blood pressure in other experimental animals, and the following conclusions were reached. The decrease of the serum calcium level in spontaneously hypertensive rats (SHR) causes a decrease in calcium/calmodulin-dependent dopamine synthesis in the brain. The subsequent low level of brain dopamine induces hypertension. The increase in susceptibility to epileptic convulsions and the occurrence of hypertension in epileptic mice (El mice) may be linked through a lowering of calcium-dependent dopamine synthesis in the brain, and epilepsy and hypertension may be associated. Exercise leads to increases in calcium-dependent dopamine synthesis in the brain, and the increased dopamine levels induce physiological changes, including a decrease in blood pressure. Cadmium which is not distinguished from calcium by calmodulin, activates calmodulin-dependent functions in the brain, and increased dopamine levels may decrease blood pressure. In this report, our studies are considered in light of reports from many other laboratories.

A 1H-NMR comparison of calmodulin activation by calcium and by cadmium

Our previous reports based on pharmacological and histochemical evidence suggest that calcium and cadmium can both activate calmodulin (CaM)-dependent functions. The study reported here was carried out to explain these observations in molecular terms, using 400 MHz 1H-NMR. Changes in the spectrum of bovine brain CaM induced by 0 to 4 molar equivalents of calcium and cadmium were practically the same. In particular, the chemical shifts and line shape of signals due to Tyr-138, Phe-65, Phe-89 and Tml-115 were similarly affected by either ion. In addition, the effects of N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide (W-7, a CaM antagonist) on the phenylalanine aromatic regions, methionine methyl regions and high-field methyl regions of the spectra of both calcium- and cadmium-saturated proteins were practically identical. The effect of W-7 on calcium- and cadmium-saturated CaM was reflected in changes in the signals of Ile-27, Phe-68, Phe-92, Ile-100 and Val-142, as well as Met-71, Met-72, Met-76, Phe-89 and Phe-141. The results show that cadmium binds to all calcium-binding sites of CaM, and induces conformational changes that are as extensive as those brought about by calcium. W-7 also inhibits CaM activation by calcium and cadmium. Combined with our previous toxicological evidence, these results suggest that cadmium binds indiscriminately to CaM and that subsequent activation or modulation of CaM-dependent functions is confused as a result. This may be a mechanism contributing to cadmium poisoning.

A mechanism of cadmium poisoning: the cross effect of calcium and cadmium in the calmodulin-dependent system

The effects of the intraventricular (IVT) administration of cadmium on the amount of dopamine (DA) in various regions of the mice brain were analyzed immunohistochemically using a microphotometry system. DA levels in the neostriatum and nucleus accumbens were increased by approximately 30% (p less than 0.01) by the IVT administration of CdCl2 (1 mumol/kg). This effect was abolished by the calmodulin antagonist, W-7 (4.2 micrograms/mouse, IVT). The effects of cadmium on DA levels in the brain were very similar to those seen with calcium. Combining these results with our previous finding that calmodulin does not have the ability to distinguish between calcium and cadmium, a mechanism of cadmium poisoning is suggested in which cadmium activates catecholamine synthesizing enzyme and numerous other enzymes through calmodulin-dependent systems, thereby disturbing many functions in the organism.