MORPHOLOGY OF CULTURED RENOMEDULLARY INTERSTITIAL CELLS

John Mathews, D. W. DuCharme and Marsha McCandlis Research Laboratories

The Upjohn Company, Kalamazoo, MI 49001

I t has been proposed that the natural antihypertensive function of the kidney is provided by the renomedullary interst i t ia l (RMI) cells. These RMI cells are highly granulated and the hypertensive state of the animal can be shown to vary with the number of granules. Cultured RMI cells, when transplanted subcutaneously into hyperten- sive animals, have been shown to have antihypertensive activity.

The RMI cells studied were grown in continuous culture from a culture received from Baptist Memorial Hospital, Memphis, Tennessee. When harvested for electron microscopy, cells were removed from the flask with trypsin, centrifuged, resuspended in buffered media, centrifuged, and the pellet placed in 2% glutaraldehyde. Subsequent osmium tetroxide fixation, dehydration and embedment were performed according to standard methods. An unusual property of these cul- tured RMI cells was the strong cell-to-cell attachment as witnessed by the fact that the fixed pellet of cells could be handled as though i t were a piece of organized tissue.

The strong cell-to-cell attachment was seen not as alignment of plasma membranes in close apposition, but rather as entanglement of the numerous microvi l l i . Rarely was an isolated cell found. Cells contained a multilobed nucleus and a large number of granules usually found near the plasma membrane. Many granules were com- pound, apparently formed from several smaller granules. Lipid droplets were numerous as were multilamellar bodies, indicating a possible storage problem concerning neutral l ipid and phospholipid. Golgi were prominent and numerous. Rough endoplasmic reticulum was abundant, but seemed dilated slightly.

Five days after transplant of RMI cells into hypertensive animals, nodules at the inoculation site were teased apart and the cells cultured. These recovered cultures showed many of the same features as the original RMI cell culture, namely, the multilobed nuclei, granules, micro- v i l l i , multilamellar bodies, rough endoplasmic reticulum and Golgi. Mitochandria had few, poorly defined cristae and var iabi l i ty in density of matrix.

A culture of high passage number which lost i ts antihypertensive function showed a much different picture with smoother nuclei, few microvil l i and few, i f any, granules. We are anticipating the examination of the current culture at high passage level to verify this observation.

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186 J. Mathews, D. W. DuCharme and M. McCandlis

Figure I .

Figure 2.

Cultured RMI ce l l s . Note numerous m i c r o v i l l i , mul t i - lobed nuclei and large number of granules.

Cell recovered by cul ture from inoculat ion s i te nodule. Many of the features seen in Figure I are present in th is ce l l . Index mark equals one micrometer.