G McClellan

Approximately 60-70% of the total fiber calcium was localized in the terminal cisternae (TC) in resting frog muscle as determined by electron-probe analysis of ultrathin cryosections. During a 1.2 s tetanus, 59% (69 mmol/kg dry TC) of the calcium content of the TC was released, enough to raise total cytoplasmic calcium concentration by approximately 1 mM. This is equivalent to the concentration of binding sites on the calcium-binding proteins (troponin and parvalbumin) in frog muscle. Calcium release was associated with a significant uptake of magnesium and potassium into the TC, but the amount of calcium released exceeded the total measured cation accumulation by 62 mEq/kg dry weight. It is suggested that most of the charge deficit is apparent, and charge compensation is achieved by movement of protons into the sarcoplasmic reticulum (SR) and/or by the movement of organic co- or counterions not measured by energy dispersive electron-probe analysis. There was no significant change in the sodium or chlorine content of the TC during tetanus. The unchanged distribution of a permeant anion, chloride, argues against the existence of a large and sustained transSR potential during tetanus, if the chloride permeability of the in situ SR is as high as suggested by measurements on fractionated SR. The calcium content of the longitudinal SR (LSR) during tetanus did not show the LSR to be a major site of calcium storage and delayed return to the TC. The potassium concentration in the LSR was not significantly different from the adjacent cytoplasmic concentration. Analysis of small areas of I-band and large areas, including several sarcomeres, suggested that chloride is anisotropically distributed, with some of it probably bound to myosin. In contrast, the distribution of potassium in the fiber cytoplasm followed the water distribution. The mitochondrial concentration of calcium was low and did not change significantly during a tetanus. The TC of both tetanized and resting freeze-substituted muscles contained electron-lucent circular areas. The appearance of the TC showed no evidence of major volume changes during tetanus, in agreement with the estimates of unchanged (approximately 72%) water content of the TC obtained with electron-probe analysis.

Inductively coupled plasma (ICP) etch rates for GaN are reported as a function of plasma pressure, plasma chemistry, rf power, and ICP power. Using a Cl2/H2/Ar plasma chemistry, GaN etch rates as high as 6875 Å/min are reported. The GaN surface morphology remains smooth over a wide range of plasma conditions as quantified using atomic force microscopy. Several etch conditions yield highly anisotropic profiles with smooth sidewalls. These results have direct application to the fabrication of group-III nitride etched laser facets.

Treatment of rat ventricular cells with 10 mM EGTA makes the sarcolemma highly permeable to small ions and molecules without removing its restriction of the diffusion of larger molecules or inactivating all of its enzymatic functions. These hyperpermeable cardiac cells have been used to study the regulation of the range of concentration of Ca over which activation of the contractile proteins occurs (Ca sensitivity). The Ca sensitivity can varied from three- to sixfold without any significant alteration in the general shape of the relation between force and Ca concentrations. Although cyclic nucleotides in concentrations of 10(-9) to 10(-5) M do not influence Ca sensitivity, in the presence of a phosphodiesterase inhibitor, cGMP increases and cAMP decreases Ca sensitivity. Treatment of the hyperpermeable cells with a nonionic detergent raises Ca sensitivity as does removal of the phosphate donor by complete substitution of CTP for ATP. These data indicate that Ca sensitivity is probably modulated by a cAMP-dependent phosphorylation that decreases Ca sensitivity. The sarcolemma is required for this reaction to take place. The effect of this reaction is antagonized by a cGMP-dependent reaction occurring inside the cell. Studies involving the perfusion of the heart with and without epinephrine before the exposure to EGTA indicate that epinephrine can regulate this system of control of Ca sensitivity. The functional considerations of this regulatory system are discussed.

Electron probe analysis, cryo-ultramicrotomy, and freeze-substitution were used to determine the nature of vacuolation and the subcellular composition in fatigued frog skeletal muscle fibers. The vacuoles caused by fatigue were part of the T-tubule system and contained high concentrations of NaCl. The calcium concentration in the terminal cisternae was higher than previously measured normal resting values. Mitochondrial calcium content was relatively low (mean +/- SEM, 2 +/- 2 mmol/kg dry weight). Fiber NaCl was increased. It is concluded that fatigue is not due to the depletion of calcium stores from the terminal cisternae or to uncoupling of mitochondria due to calcium loading but may be caused by multiple mechanisms including failure of the T-tubule action potential.

Inductively coupled plasma (ICP) etching of GaAs, GaP, and InP is reported as a function of plasma chemistry, chamber pressure, rf power, and source power. Etches were characterized in terms of rate and anisotropy using scanning electron microscopy, and root-mean-square surface roughness using atomic force microscopy. ICP etch rates were compared to electron cyclotron resonance etch rates for Cl2/Ar, Cl2/N2, BCl3/Ar, and BCl3/N2 plasmas under similar plasma conditions. High GaAs and GaP etch rates (exceeding 1500 nm/min) were obtained in Cl2-based plasmas due to the high concentration of reactive Cl neutrals and ions generated as compared to BCl3-based plasmas. InP etch rates were much slower and independent of plasma chemistry due to the low volatility of the InClx etch products. The surface morphology for all three materials was smooth over a wide range of etch conditions.