Mechanisms of P(i) regulation of the skeletal muscle SR Ca(2+) release channel.

Inorganic phosphate (P(i)) accumulates in the fibers of actively working muscle where it acts at various sites to modulate contraction. To characterize the role of P(i) as a regulator of the sarcoplasmic reticulum (SR) calcium (Ca(2+)) release channel, we examined the action of P(i) on purified SR Ca(2+) release channels, isolated SR vesicles, and skinned skeletal muscle fibers. In single channel studies, addition of P(i) to the cis chamber increased single channel open probability (P(o); 0.079 +/- 0.020 in 0 P(i), 0. 157 +/- 0.034 in 20 mM P(i)) by decreasing mean channel closed time; mean channel open times were unaffected. In contrast, the ATP analog, beta,gamma-methyleneadenosine 5'-triphosphate (AMP-PCP), enhanced P(o) by increasing single channel open time and decreasing channel closed time. P(i) stimulation of [(3)H]ryanodine binding by SR vesicles was similar at all concentrations of AMP-PCP, suggesting P(i) and adenine nucleotides act via independent sites. In skinned muscle fibers, 40 mM P(i) enhanced Ca(2+)-induced Ca(2+) release, suggesting an in situ stimulation of the release channel by high concentrations of P(i). Our results support the hypothesis that P(i) may be an important endogenous modulator of the skeletal muscle SR Ca(2+) release channel under fatiguing conditions in vivo, acting via a mechanism distinct from adenine nucleotides.

Chloride-dependent sarcoplasmic reticulum Ca2+ release correlates with increased Ca2+ activation of ryanodine receptors.

The mechanism by which chloride increases sarcoplasmic reticulum (SR) Ca2+ permeability was investigated. In the presence of 3 microM Ca2+, Ca2+ release from 45Ca(2+)-loaded SR vesicles prepared from procine skeletal muscle was increased approximately 4-fold when the media contained 150 mM chloride versus 150 mM propionate, whereas in the presence of 30 nM Ca2+, Ca2+ release was similar in the chloride- and the propionate-containing media. Ca(2+)-activated [3H]ryanodine binding to skeletal muscle SR was also increased (2- to 10-fold) in media in which propionate or other organic anions were replaced with chloride; however, chloride had little or no effect on cardiac muscle SR 45Ca2+ release or [3H]ryanodine binding. Ca(2+)-activated [3H]ryanodine binding was increased approximately 4.5-fold after reconstitution of skeletal muscle RYR protein into liposomes, and [3H]ryanodine binding to reconstituted RYR protein was similar in chloride- and propionate-containing media, suggesting that the sensitivity of the RYR protein to changes in the anionic composition of the media may be diminished upon reconstitution. Together, our results demonstrate a close correlation between chloride-dependent increases in SR Ca2+ permeability and increased Ca2+ activation of skeletal muscle RYR channels. We postulate that media containing supraphysiological concentrations of chloride or other inorganic anions may enhance skeletal muscle RYR activity by favoring a conformational state of the channel that exhibits increased activation by Ca2+ in comparison to the Ca2+ activation exhibited by this channel in native membranes in the presence of physiological chloride (< or = 10 mM). Transitions to this putative Ca(2+)-activatable state may thus provide a mechanism for controlling the activation of RYR channels in skeletal muscle.

Genetic contributions to saliva protein concentrations in adult human twins.

The heritability of saliva protein concentrations was investigated in stored samples of clarified stimulated whole saliva from adult twins participating in a study of periodontal disease genetics. Saliva was obtained from 29 monozygous and 20 dizygous twin pairs. Visits were scheduled so that both twins in a pair donated saliva at the same time of day. Flow rate was determined, and frozen samples later assayed for lactoferrin, lysozyme, secretory IgA, total peroxidase, myeloperoxidase and total protein. Pairs were always assayed together. Within- and between-pair variances were used to estimate twin intraclass correlations. Pearson correlations were used to estimate associations between saliva variables and clinical indices of gingivitis, dental plaque, periodontal attachment loss, and probing depth. Significant genetic contributions to variance were seen for total protein, lactoferrin, and total peroxidase. Total protein showed a significant positive correlation with gingivitis. There were no other correlations with clinical indices, and intraclass correlations for saliva variables did not change after adjustment for gingivitis. Dizygous twin correlations were higher than monozygous twin correlations for flow rate, lysozyme, and secretory IgA. That may be an artefact due to small numbers of pairs. It seems unlikely that a common environmental factor would strongly affect saliva in twins living apart as adults. Present findings, taken as sib correlations, support a genetic contribution to saliva protein concentrations. Problems with the twin model in saliva might be resolved by longitudinal studies of large numbers of twins.

Platelet-interactive products of Streptococcus sanguis protoplasts.

To isolate a more native, platelet-interactive macromolecule (class II antigen) of Streptococcus sanguis, cultured protoplasts were used as a source. Protoplasts were optimally prepared from fresh washed cells by digestion with 80 U of mutanolysin per ml for 75 min at 37 degrees C while osmotically stabilized in 26% (wt/vol) raffinose. Osmotically stabilized forms were surrounded by a 9-nm bilaminar membrane, as shown by transmission electron microscopy. Protoplasts were cultured in chemically defined synthetic medium and osmotically stabilized by ammonium chloride. Spent culture media were harvested daily for 7 days. Each day, soluble proteins were isolated from media, preincubated with platelet-rich plasma, and tested for inhibition of platelet aggregation induced by S. sanguis cells. Products released from S. sanguis protoplasts and reactive with an anti-class II antigen immunoaffinity matrix were able to inhibit S. sanguis-induced platelet aggregation. As resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, anti-class II-reactive protoplast products included silver-stained bands of 67, 79, 115, 216, and 248 kDa. The 115-kDa protein fraction was isolated by gel filtration and ion-exchange chromatography. This form of the class II antigen contained N-formylmethionine at its amino terminus. Rhamnose constituted 18.2% of the total residual dry weight and nearly half of its carbohydrate content. Diester phosphorus constituted 1% of this fraction. After trypsinization of the protoplast products from either preparation, a 65-kDa protein fragment was recovered. This protoplast protein fragment and the S. sanguis cell-derived 65-kDa class II antigen, previously implicated in the induction of platelet aggregation, were shown to be functionally and immunologically identical.

Faculty and administrator perceptions of decision making.

This research study was conducted in associate and baccalaureate schools of nursing. This research focused on the extent of faculty participation in decision making; a description and analysis of the characteristics of nurse faculty, nurse administrators, and the organizations of associate and baccalaureate schools of nursing; the interrelationships between opportunities for participation in decision making and the level and type of decision making; the relationships between various personal and situational variables that affect decision making, the relationship between the type of involvement in decision making to the variables of job satisfaction, professional commitment, and job tension; and the relationships among the variables of job satisfaction, professional commitment and job tension. Ninety-three faculty and 10 administrators participated in the research study. Research data were collected by three instruments: the School Information Profile, the Administrative Questionnaire, and the Faculty Questionnaire. The data were subjected to frequency distribution statistics, the RELIABILITY program of SPSS, Pearson correlation coefficients, Canonical correlations, and Multiple Regression analysis. The primary study results were: Faculty reported that their participation in decision making is primarily in the area of making recommendations, not final determinations. Faculty stated that decision making is usually a group process. Administrator perceptions were that faculty possess more decision-making power than faculty believed. Faculty reaffirmed that job satisfaction and professional commitment are positively correlated, and that job tension was found to be negatively correlated to job satisfaction and professional commitment.(ABSTRACT TRUNCATED AT 250 WORDS)