The cellular distribution of calcium in freeze-dried rabbit vas deferens using EM autoradiography

Effects of temperature and buffer composition on calcium sequestration by sarcoplasmic reticulum and plasma membrane of rabbit renal artery

45Ca electron microscopic autoradiography was used to examine the effects of buffer composition and temperature on the distribution of calcium in rabbit renal artery smooth muscle cells. The results show that the relative distribution of calcium is dependent on both the buffer used (Tris or Krebs) and the temperature of the bathing solution (25 degrees C or 34 degrees C). Krebs buffer at 34 degrees C gave the highest relative activity in the plasma membrane, sarcoplasmic reticulum, and mitochondria. Buffer and temperature had little effect on the relative activity of the nucleus or cytoplasm. Next, we identified the cellular sites of calcium accumulation after 5, 15, 30, or 60 min exposure to 45Ca in Krebs buffer at 34 degrees C. The results show that sarcoplasmic reticulum and plasma membrane are the primary sites of calcium accumulation during influx into these cells. Although the amount of 45Ca in the cell continues to increase with longer exposure, the relative distribution of calcium is essentially the same after 5 or 60 min. The data also indicate that the relative activity of plasma membrane + sarcoplasmic reticulum (a combination site that includes sarcoplasmic reticulum within a mean distance of 275 nm of the plasma membrane) is similar to the membrane alone and is lower than the sarcoplasmic reticulum alone.

Localization of calcium in vas deferens using 45Ca EM autoradiography: relationship to species and the effect of 45Ca removal

The distribution of calcium was determined in the vas deferens of the guinea pig using 45Ca electron microscopic autoradiography of rapidly frozen, freeze-dried, and embedded tissue. A selective accumulation of calcium at the plasma membrane and SR was observed in vas deferens that had been incubated in 45Ca for 65-85 min prior to rapid freezing. Rinsing the tissue in nonradioactive calcium for 6 min prior to rapid freezing significantly altered the distribution of calcium among the plasma membrane, mitochondria, and cytoplasmic matrix. The influence of species on the observed distribution of calcium was also examined. The distribution of calcium in the guinea pig vas deferens was not significantly different from that in the rabbit vas deferens when the tissues were prepared under identical conditions.

Statistical significance tests for autoradiographic data

The purpose of this paper is to develop statistical methods that take radiation spread into account in analyzing data from different autoradiographic experiments. The method uses the probability circle analysis of Salpeter and McHenry (1973) to obtain the probable source of each radioactive emission and the circle and point counting method of Williams (1969) to estimate the relative area occupied by each cellular site. Two levels of analysis are presented. The first level of analysis is concerned with estimating relative activities and standard errors for cellular items that are larger than the probability circle. The second level of analysis involves estimating relative activities and standard errors for cellular sites that are smaller than the probability circle and are therefore observed in circles containing another item such as cytoplasmic matrix. Two different tests of hypotheses are discussed. The first null hypothesis is that the radioactivity is randomly distributed among the cellular sites. The second null hypothesis is that there is no difference between two different treatments in the relative activities for a given site.