Key result
Freeze-dried guinea pig vas deferens smooth muscle cells showed calcium accumulation in the plasma membrane, mitochondria, and sarcoplasmic reticulum, with twice the cross-sectional area of conventional cells.
Freeze-drying combined with electron microscope autoradiography demonstrates that the plasma membrane, mitochondria, and sarcoplasmic reticulum in guinea pig vas deferens smooth muscle can accumulate calcium, while also revealing structural differences compared to conventional preparation.
No clinical implications; extends ultrastructural calcium mapping in animal smooth muscle but leaves open human relevance.
In an effort to more clearly elucidate the role of cellular structures as calcium sinks and sources in smooth muscle cells, the intracellular distribution of radioactive calcium was evaluated by a new method based on freeze-drying. The guinea pig vas deferens was exposed to a physiological salt solution that contained 45Ca. The muscle was then freeze-dried and prepared for electron microscope autoradiography. The grain density over the plasma membrane, mitochondria, and sarcoplasmic reticulum (SR) was significantly greater than that of the matrix. These results suggest that the plasma membrane, mitochondria and SR have the capacity to accumulate calcium. Which of these structures serve as a source of calcium for contraction remains to be determined. A stereological comparison between freeze-dried and conventionally prepared smooth muscles revealed several differences. The cross-sectional area of freeze-dried cells was about twice that of conventionally prepared cells. Moreover, mitochondria and sub-surface vesicles occupied a significantly smaller percentage of the cell in the freeze-dried tissue than they did in the conventionally prepared tissue.
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McGuffee et al. (1981) studied this question. Freeze-drying method vs. Conventionally prepared smooth muscles was evaluated on Intracellular distribution of radioactive calcium and stereological comparison. Freeze-dried guinea pig vas deferens smooth muscle cells showed calcium accumulation in the plasma membrane, mitochondria, and sarcoplasmic reticulum, with twice the cross-sectional area of conventional cells.
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