Calmodulin activation of adenylate cyclase in the mouse B16 melanoma

Calmodulin antagonists inhibited hormone-stimulated cyclic AMP accumulation in both cultured cells and cell lysates of mouse B16 melanoma. Particulate preparations of B16 melanoma contained 34-45% of total cell calmodulin, which could not be dissociated by extensive washing irrespective of the presence of EGTA in the buffer. The adenylate cyclase activity in such preparations was unaffected by the addition of exogenous calmodulin. However, the rare-earth-metal ion La3+, which can mimic or replace Ca2+ in many systems, produced an immediate inhibition of agonist-stimulated adenylate cyclase activity and preincubation of particulate preparations was La3+ followed by washing with La3+-free buffer dissociated calmodulin (96% loss) from particulate preparations. The loss of calmodulin from particulate preparations was associated with a decrease in agonist responsiveness (74%) and a marked change in the Ca2+-sensitivity of the enzyme, low concentrations of calcium (approx. 10 nM) now failing to stimulate enzyme activity, high concentrations of calcium (greater than or equal to 100 nM) producing greater-than-normal inhibition of enzyme activity. Direct activation of adenylate cyclase by the addition of pure calmodulin was now demonstrable in such calmodulin-depleted particulate preparations. Half-maximal stimulation of agonist-responsive adenylate cyclase occurred at 80 nM-calmodulin in the presence of 10 microM free Ca2+. Maximal stimulation by calmodulin (at 300-600 nM) restored enzyme activity to 89 +/- 5% (mean +/- S.E.M., n = 7) of the activity in untreated, calmodulin-intact, preparations.

Studies on the involvement of calcium and calmodulin in the action of growth-hormone-releasing factor

A possible role for Ca2+ and calmodulin in the action of growth-hormone-releasing factor (GHRF) was investigated. Low extracellular Ca2+ (less than 100 microM), methoxyverapamil, flunarizine, cinnarizine, and Co2+ decreased both basal and GHRF-stimulated growth-hormone secretion, but did not totally inhibit GHRF-stimulated secretion. A calmodulin antagonist, W7, abolished GHRF-stimulated GH secretion, with no effect on basal secretion. It is suggested that GHRF may act primarily by elevating cellular cyclic AMP, which may then modulate calcium mobilization or flux; the increased intracellular Ca2+ concentrations may then activate calmodulin.

Nature and boundaries of phonologic categories: a case study of an unusual phonologic pattern in a language-impaired child

This paper presents a detailed examination of an unusual phonologic pattern reflected in the speech of a language-impaired child. The most salient characteristic of this child's speech was the use of [s] in final position of all words except those containing final oral or nasal bilabials. Her pattern seemed best described as reflecting only two canonical forms for word production, CVC and CVCVC, and a dominant word-final category possessing a family resemblance structure with [s] as the prototype. Training was instituted to increase the number of appropriate categories in the child's phonologic system. Training on word-final [f] and [d] was successful. However, training on [d] seemed to result in the creation of a second category with family resemblance structure. The clinical and theoretical implications of this child's phonologic pattern are discussed.

Pertussis toxin blocks the inhibitory effect of muscarinic cholinergic agonists on cyclic AMP accumulation and prolactin secretion in GH3 anterior-pituitary tumour cells

The inhibition of prolactin secretion and cyclic AMP accumulation in GH3 cells by muscarinic agonists was blocked by preincubation of the cells with pertussis toxin (islet-activating protein). There was a lag of approx. 80 min in the onset of the effect on secretion. These results suggest that muscarinic agonists decrease prolactin secretion by inhibiting adenylate cyclase activity.

Muscarinic acetylcholine receptor activation causes inhibition of cyclic AMP accumulation, prolactin and growth hormone secretion in GH3 rat anterior pituitary tumour cells

Acetylcholine, oxotremorine and carbachol, compounds that exhibit muscarinic agonist activity, maximally inhibited basal prolactin secretion from GH3 cells by approx. 50% and intracellular cyclic AMP levels by approx. 20%. Both parameters were inhibited with similar potencies by each agonist. These inhibitory effects were blocked by a muscarinic but not by a nicotinic receptor antagonist. In the presence of VIP or IBMX, which raise intracellular cyclic AMP levels and stimulate hormone release, the degree of muscarinic inhibition was increased, but the potency remained unchanged. Similar changes in the secretory rate of prolactin and growth hormone occurred in these and in cell perifusion experiments. These results suggest that the inhibition of hormone secretion from GH3 cells by muscarinic agonists is mediated by a decrease in intracellular cyclic AMP levels.

Flunarizine, a calcium influx blocker, inhibits TRH-but not potassium-stimulated prolactin secretion

The effect of flunarizine on the secretion of prolactin from monolayer cultures of normal rat pituitary cells has been determined. Both basal and TRH-stimulated secretion were found to be significantly inhibited by micromolar concentrations of flunarizine, whereas depolarization (high K+)-stimulated secretion was virtually unaffected. These results indicate that TRH-stimulated prolactin secretion probably involves calcium influx and that flunarizine may be useful as a probe for particular Ca2+ channels.

The possible involvement of both calcium and cyclic AMP in the dopaminergic inhibition of prolactin secretion

Dopamine inhibited basal, TRH-, IBMX- and A23187-stimulated prolactin secretion from rat anterior pituitary cells. However, dopamine did not inhibit prolactin secretion stimulated by elevated K+ concentrations. These data are interpreted in terms of dopaminergic inhibition of both cyclic AMP production and Ca2+ influx through agonist-, but not voltage-, dependent Ca2+ channels.

An investigation of the involvement of calcium in the control of prolactin secretion: studies with low calcium, methoxyverapamil, cobalt and manganese

The possible role of calcium as a primary mediator in the control of prolactin secretion from normal pituitary cells was examined. Basal prolactin secretion, and secretion stimulated by thyrotrophin releasing hormone (TRH), raised K+ or the calcium ionophore, A23187, were all dependent on the presence of extracellular Ca2+. The calcium channel antagonists, methoxyverapamil, cobalt and manganese, inhibited basal, TRH- and K+-stimulated prolactin secretion. In addition, prolactin secretion stimulated by a phosphodiesterase inhibitor, isobutylmethylxanthine, which increases cellular cyclic AMP, was inhibited by these Ca2+ antagonists. These observations indicate that Ca2+ may be the primary intracellular mediator in the control of prolactin secretion, with cyclic AMP having a secondary modulatory role on Ca2+ influx, probably on voltage-dependent Ca2+ channels.

Calmodulin and cell function

Introduction: The importance of calcium in the regulation of cell function has become increasingly recognized in the past 20 years. It is now known that changes in intracellular calcium concentration, like changes in adenosine 3′:5′-monophosphate (cyclic AMP), are of crucial importance in stimulus-response coupling. Thus, the second messenger theory originally proposed by Sutherland et al. [1], in which a hormone or nerve impulse is first messenger and cyclic AMP the second intracellular messenger, has been expanded to include calcium ions as well as cyclic nucleotides. Moreover, there is now evidence in many cellular systems that calcium ions and cyclic nucleotides act as dual interrelated messengers [2], and, therefore, some cellular processes are regulated by calcium as well as by cyclic nucleotides, as shown in Table 1. Evidence has accumulated that it is changes in free intracellular calcium concentration that are, in some way, responsible for activation of the enzymes involved in the processes shown in this Table.

Dual effects of manganese on prolactin secretion

The effect of Mn2+ (a commonly used Ca2+ antagonist) on prolactin secretion from pituitary cells was investigated. In the presence of normal extracellular Ca2+ levels (2.5mM), Mn2+ inhibited basal, TRH- and K+- stimulated prolactin secretion. The Ca2+ ionophore, A23187, partially overcame the inhibitory effect of Mn2+. However, in the presence of low extracellular Ca2+ (less than 100 microM), which decreased basal prolactin secretion and abolished any stimulatory effects of TRH or K+, a paradoxical stimulatory effect was observed with Mn2+ in the presence of A23187. In the presence of Ca2+, Mn2+ appeared to be inhibitory due to its Ca2+ antagonistic effects, but at low Ca2+ levels, intracellular stimulatory effects of Mn2+ became apparent.

Isolation, purification and cell-free synthesis of calmodulin from the pig anterior pituitary gland

Calmodulin was extracted and purified from pig anterior pituitary gland. The protein was characterized by its migration on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis in the presence of Ca2+ or EGTA, its U.V. spectrum between 240 and 290 nm and the activation of calmodulin-deficient cyclic AMP phosphodiesterase. The yield was 370 mg/kg wet wt. mRNA was also extracted from the same tissue and translated in a wheat-germ cell-free translation system. Translated calmodulin was identified by its heat-stability, its co-migration with authentic anterior-pituitary calmodulin on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, its acidic isoelectric point (4.15) on flat-bed isoelectric focusing, its Ca2+-dependent binding to fluphenazine-Sepharose 6B, and its co-elution from this gel with authentic unlabelled calmodulin with EGTA buffer. Calmodulin was not translated as a precursor form. In this tissue it was calculated that calmodulin accounted for 0.5-1% of the total translated protein.

Thyrotropin-releasing hormone stimulates inositol phosphate production in normal anterior pituitary cells and GH3 tumour cells in the presence of lithium

Phosphatidylinositol (Ptd Ins) breakdown in response to thyrotropin-releasing hormone (TRH) was measured after preincubation of both normal rat anterior pituitary cells and GH3 tumour cells with [3H]inositol by the determination of [3H]inositol phosphate accumulation in the presence of lithium (which inhibits myo-inositol phosphatase). The method employed, which was originally developed for use with tissue slices, was adapted for isolated cells in monolayer culture. In GH3 cells, TRH stimulated the breakdown of phosphoinositide in a manner similar to that reported previously using alternative methods. Furthermore, in normal male anterior pituitary cells the dose-response profile for TRH stimulation of inositol phosphate accumulation was found to correlate well with the dose-response profile for TRH stimulation of prolactin secretion. As this response was maintained in the absence of added calcium, the breakdown of phosphoinositide would appear to be implicated as an event preceding calcium mobilization.

A possible role for calmodulin in human thyroid cell metabolism

A protein which shared several characteristics with authentic calmodulin was extracted from human thyroid homogenates. The protein bound to fluphenazine--Sepharose and could be specifically eluted using EGTA. The eluted protein had a u.v. spectrum characteristic of calmodulin and migrated like authentic calmodulin with a calcium-dependent shift on sodium dodecyl sulphate polyacrylamide-gel electrophoresis. Calmodulin in thyroid cell extracts was shown to be biologically active, measured by its ability to activate a calmodulin-deficient cyclic GMP phosphodiesterase; this activation could be inhibited by trifluoperazine. A possible role for calmodulin in the action of TSH on the thyroid was demonstrated by studying the effects of phenothiazines and the naphthalene sulphonamide, W7, a more specific calmodulin inhibitor, on TSH-stimulated cyclic AMP levels in cultured thyroid cells. The phenothiazines and W7 were found to inhibit the accumulation of cyclic AMP in response to TSH in a concentration-dependent manner although low concentrations of W7 enhanced TSH-stimulated cyclic AMP accumulation.

The relationship between prolactin secretion and calmodulin activity

The possible role of calmodulin in the control of prolactin secretion was examined. The effects of a wide variety of agents on inhibition of prolactin secretion from isolated rat anterior pituitary cells and inhibition of calmodulin activity in an in-vitro system (calmodulin-activated cyclic GMP phosphodiesterase) were compared. A number of phenothiazines showed a close correlation of potencies in the two systems, as did the more specific calmodulin antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalene sulphonamide (W7), suggesting that calmodulin may be involved in the control of prolactin secretion. Some other drugs also inhibited both prolactin secretion and calmodulin activity in addition to their other well-characterized biochemical effects. However, many of these drugs (including two phenothiazines) were more potent inhibitors of prolactin secretion than of calmodulin activity, suggesting that other intracellular systems in addition to calmodulin may be involved in the control of the secretory process.

The possible role of calmodulin in the inhibition of prolactin secretion by dopaminergic antagonists

Several previous reports have indicated that a number of dopaminergic antagonists paradoxically inhibit prolactin secretion at micromolar concentrations. It is well known that some of these drugs, including pimozide and the phenothiazines, are inhibitors of calmodulin activity. Here we report that micromolar concentrations of several dopaminergic antagonists inhibit prolactin secretion from isolated rat anterior pituitary cells and calmodulin activity (calmodulin-activated cyclic GMP phosphodiesterase). Inhibition of calmodulin activity may thus, at least partially, explain the inhibitory effect of these drugs on prolactin secretion.

Evidence that calmodulin may be involved in phytohaemagglutinin-stimulated lymphocyte division

Phytohaemagglutinin-stimulated and non-stimulated incorporation of [3H]thymidine into human peripheral blood lymphocytes is inhibited by the calcium antagonist PY 108–068 and by the calmodulin antagonists trifluo-perazine and N-(6-aminohexyl)-5-chloro-l-naphthalene sulphonamide (W7). It is argued that calmodulin may be involved in both non-stimulated [3H]thymidine uptake in lymphocytes and also in the lymphocyte response to phytohaemagglutinin.

The determination of the sex of an individual from a dried bloodstain using radioimmunoassay of testosterone, progesterone, and estradiol-17 beta

A radioimmunoassay (RIA) technique was developed for the purpose of determining the sex of an individual by measuring the steroids testosterone (T), progesterone (P), and estradiol-17 beta (E2) in dried bloodstains. The steroid values from a single bloodstain are reported as ratios T/P, T/E2, and P/E2. The results reported include data on the validation of this technique, results of analysis of 146 duplicate bloodstains representing 112 samples from females and 34 samples from males as controls, and results of analysis of 114 duplicate bloodstains representing 60 from females and 54 from males that were submitted as a blind study to test the accuracy of this RIA technique in determining the sex of an individual from a dried bloodstain.

Lack of effect of angiotensin on levels of cyclic AMP in isolated adrenal zona glomerulosa cells from the rat

The effects of pure [Asp1,Val5]- and [Asn1,Val5]-angiotensin II and also [des-Asp1,Ile5]-angiotensin II (angiotensin III) on cyclic AMP and steroid outputs by dispersed rat capsular cells, comprising 95% zona glomerulosa and 5% zona fasciculata cells, have been studied. The results showed that [Asp1, Val5]-and [Asn1, VAl5]-angiotensin II, at doses between 2.5 X 10(-11) and 2 X 10(-4) mol/l, which produced typical increases in steroidogenesis, failed to increase output of cyclic AMP. This lack of effect was observed whether the nucleotide was measured by radioimmunoassay or by adrenal binding protein and under the same conditions in which 8.4 mM-K+ consistently increased the output of cyclic AMP. Instead the results showed a small but significant decrease in cyclic AMP output with angiotensin II. Similar results were obtained with incubations for 60 rather than 120 min and with medium containing a concentration of 5 or 40 g bovine serum albumin/l. Although the levels of cyclic AMP were generally higher in the presence of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, the same decrease relative to basal outputs was observed with angiotensin II which increased steroidogenesis. Angiotensin III also failed to increase output of cyclic AMP at doses (2.5 X 10(-9) to 2.5 X 10(-6) mol/l) which produced increases in steroid output equivalent to those with angiotensin II. These results indicate that angiotensin II and III can act through a cyclic AMP-independent mechanism.